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fix(frontend): stop tool_call_dispatch handing harnesses truncated arguments - #13986
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Automated evidence record — validation incompleteValidation status: incomplete Evidence summary: [3/4 validated · 1 missing dep] AI review assessment: sound — advisory only. This is an AI agent's judgment of whether the Validation result: incomplete. Three of the four recorded recipes validated. The fourth, Evidence audit: complete [3/4 validated · 1 missing dep] — the evidence table below is Evidence [3/4 validated · 1 missing dep]Generated from validation/registry.jsonl — do not edit by hand.
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plan.md# Plan — ai-dynamo/dynamo#13972: `tool_call_dispatch` cannot safely reconstruct fragmented arguments
Route: implementation
Template: model-parser-investigation
Engine: vllm
## User intent
The caller asked us to address <https://github.com/ai-dynamo/dynamo/issues/13972>, an OPEN
bug labelled `bug`, `language::rust`, `backend::vllm`, `frontend`. The Slack thread carries
nothing but the issue link, so the issue body is the whole brief — and it is an unusually
prescriptive one. It does not merely report that the opt-in `event: tool_call_dispatch`
extension mishandles split tool calls; it specifies the replacement design in four numbered
sections and enumerates twelve regression cases.
Stated plainly: Dynamo's Chat Completions streaming path currently decides that a tool call
is "complete" by looking at a single delta chunk in isolation. If one chunk carries `id`,
`function.name`, and any `Some(arguments)` — including `Some("")` or a truncated prefix like
`{"path":"/a/very` — it emits the dispatch event immediately and then permanently suppresses
that call via a `(choice_index, id)` dedup set. The caller wants that same-chunk assumption
replaced with genuine request-local assembly: accumulate per `(choice.index,
tool_call_chunk.index)`, merge identity fields first-wins, concatenate argument fragments,
and emit exactly once at a defined JSON completion boundary — with the ordinary OpenAI
`data:` stream passing through byte-for-byte unchanged and the extension staying opt-in.
The urgency is concrete rather than theoretical: issue #13821 (OPEN) will restore normal
OpenAI delta cadence in the Python vLLM postprocessor, at which point long string arguments
stop arriving in one frame and the current dispatcher starts emitting truncated JSON to
agent harnesses that will try to execute it.
## Non-goals
- **The Python vLLM postprocessor delta cadence.** That is #13821, explicitly carved out by
the issue's Scope section. This work item touches only the Rust side.
- **Changing `DeltaAggregator`'s merge semantics.** The aggregator's first-wins identity
policy silently ignores a conflicting later value. The dispatcher must fail closed on a
conflict; the aggregator must keep behaving exactly as it does today. #8582/#8640 shipped
that behavior and regressing it to satisfy this issue would be scope creep.
- **Parser-v2 Qwen streaming**, whose scanner waits for a complete `</function>` block, and
the **Responses / Anthropic converters**, which have their own protocol completion events.
- **Making `tool_call_dispatch` part of the standard OpenAI stream.** It stays behind
`--enable-streaming-tool-dispatch` / `DYN_ENABLE_STREAMING_TOOL_DISPATCH`, default false.
- **Tool-schema validation or execution authorization.** The issue is explicit that
successful `serde_json` parsing proves syntax only; the extension client keeps that duty.
- **Reviving PR #6845's stream adapter or its `event: tool_call.complete` boundary.**
- **Restoring the buffered-until-`finish_reason` behavior.** Early dispatch is the feature.
## Discovery
### The code as it stands today
I read `lib/llm/src/http/service/openai.rs` in the checkout at `b4338ab87`. Line numbers in
the issue are against `ff18f721` and have drifted; I located everything by symbol.
`streaming_tool_dispatch_events` (currently openai.rs:2646-2681) is a free function taking
`&Annotated<NvCreateChatCompletionStreamResponse>`, `&mut HashSet<(u32, String)>`, and the
output event vector. Its predicate is exactly what the issue quotes: `has_name_and_args`
requires `f.name.is_some() && f.arguments.is_some()` on the *same* chunk, and on success it
inserts `(choice.index, id.clone())` into the dedup set and pushes the event. There is no
accumulation of any kind — the payload borrows the incoming chunk directly.
The payload type is `ToolCallDispatchPayload<'a> { choice_index: u32, tool_call: &'a
ChatCompletionMessageToolCallChunk }` (openai.rs:2548-2551), serialized by the shared
`push_dispatch_event` helper (openai.rs:2560-2571). This matters for the redesign: the event
is a borrowed view of a `ChatCompletionMessageToolCallChunk`, which is the same type the
aggregator accumulates into. Assembly state can therefore *be* a
`ChatCompletionMessageToolCallChunk` and the payload can keep borrowing — from the state map
entry rather than from the incoming chunk — with no allocation added to the hot path and no
change to the wire format the issue says must stay as-is.
The per-request streaming branch that owns the dispatch state is `chat_completions`
(openai.rs:2935-2941): `tool_dispatch_enabled`, `reasoning_dispatch_enabled`,
`reasoning_field`, `reasoning_buffer: HashMap<u32, String>`, `dispatched_tool_ids:
HashSet<(u32, String)>`, `emitted_roles: HashSet<u32>`. The new assembly state belongs
here, beside `reasoning_buffer`, and is naturally request-scoped and dropped with the stream.
The SSE loop is the `async_stream::stream!` block at openai.rs:2947-3025. Its current order
is already the order the issue's section 4 demands:
1. `enforce_single_tool_call` retains only `tc.index == 0` and nulls an emptied vector
(openai.rs:2956-2967) — so `parallel_tool_calls=false` filtering happens *before* the
dispatcher ever sees the chunk. Regression case 9 is satisfied by preserving this order,
not by adding logic inside the dispatcher.
2. `deduplicate_stream_roles`.
3. The `is_empty_stream_response` early `continue` (openai.rs:2974-2989).
4. `streaming_tool_dispatch_events`, then `accumulate_reasoning_dispatch`.
5. `EventConverter` conversion, then `events.reverse()` / `pop()` so side-channel events are
yielded before the ordinary `data:` event.
I checked step 3 specifically, because a terminal completion pass needs a chunk carrying
`finish_reason` to actually reach the dispatcher. `is_empty_stream_response`
(openai.rs:2574-2604) destructures the delta exhaustively and requires
`c.finish_reason.is_none()` among its conditions, so a finish-carrying chunk is never
dropped as empty. The terminal hook is available where it needs to be.
`accumulate_reasoning_dispatch` (openai.rs:2689-2720) is the local precedent for
request-local accumulation state: a `HashMap<u32, String>` owned by the handler, flushed on a
`Some → None` transition *or* on `finish_reason`. The tool-call state machine should read as
a sibling of it.
### The merge policy that already exists
`merge_tool_call_chunk` in `lib/llm/src/protocols/openai/chat_completions/aggregator.rs:221-254`
is a private free function implementing precisely the semantics the issue asks the dispatcher
to adopt: `id` and `r#type` first-wins, `function` adopted wholesale when absent, `name`
first-wins, and `arguments` concatenated via `get_or_insert_with(String::new).push_str(...)`.
Its doc comment names #8640 and the vLLM/SGLang hermes delta shape. `finalize_merged_tool_chunk`
(aggregator.rs:264-305) is the companion that drops a chunk with a warning when `id`,
`function`, or `name` never arrived. The regression tests the issue cites are
`test_issue_8640_split_tool_call_arguments_reconstructed` (aggregator.rs:1271) and
`test_parallel_tool_calls_interleaved_chunks_aggregate_independently` (aggregator.rs:1353),
with `test_parallel_tool_calls_false_caps_to_first_call` at aggregator.rs:1428.
I enumerated call sites. `merge_tool_call_chunk` has exactly one caller, aggregator.rs:414,
plus a doc reference at aggregator.rs:175. `streaming_tool_dispatch_events` has exactly two,
the handler at openai.rs:2991 and the test helper `collect_tool_dispatch_events` at
openai.rs:7743. Both call graphs are small and entirely inside `dynamo-llm`.
The one gap: `merge_tool_call_chunk` does *not* detect identity conflicts. It silently keeps
the first value. The issue requires the dispatcher to mark an entry invalid when a later
non-empty identity field conflicts. So extraction cannot be a pure move — the shared helper
has to report the conflict, even though the aggregator will keep ignoring it.
### Existing tests, so we do not re-specify covered ground
The dispatch tests live in openai.rs:7808-8090. Already present and passing:
`test_tool_dispatch_emits_event_for_complete_tool_call` (single-chunk happy path, the exact
payload assertion of the issue's regression case 1); three `skips_incomplete_*` cases for
missing id / name / arguments; `test_tool_dispatch_multiple_tool_calls` (inner indexes 0 and 1
in one chunk); `test_tool_dispatch_no_data`; `test_tool_dispatch_empty_choices`;
`test_tool_dispatch_mixed_complete_and_incomplete`; `test_tool_dispatch_function_none`;
`test_tool_dispatch_empty_arguments_still_dispatches` (openai.rs:8021, asserting `Some("")`
dispatches — this is the test the redesign must *change*, since section 3 moves that
behavior to the terminal pass); `test_tool_dispatch_n_greater_than_1_includes_choice_index`
(#12676/#12680); and `test_tool_dispatch_dedup_skips_already_dispatched_id` (regression
case 11, which must survive as the tombstone test).
The two helpers the issue names are exactly as described. `make_choice_with_tool_call`
(openai.rs:7777-7806) hardcodes `index: 0` on the inner `ChatCompletionMessageToolCallChunk`
while taking the *outer* choice index as its first parameter — so today it cannot express
regression case 7 at all, and every multi-inner-index test in the file
(`test_tool_dispatch_multiple_tool_calls`, `test_tool_dispatch_mixed_complete_and_incomplete`)
hand-builds its chunks instead. `extract_sse_data_json` (openai.rs:7629-7698) parses axum's
`Debug` output for `Event`, finds the JSON by a brace-depth scan with no string awareness
(openai.rs:7644-7658), then unescapes byte-string escapes by string replacement. A dispatch
payload whose `arguments` value contains a quoted `}` will terminate that scan early and the
helper will panic inside itself — which is why the issue says quoted-brace cases must assert
on typed state or real SSE serialization rather than route through it.
### Related and competing work
I ran all-state host PR searches on the issue number and on semantic identifiers —
`tool_call_dispatch`, `streaming_tool_dispatch_events`, `enable-streaming-tool-dispatch`,
`merge_tool_call_chunk`, plus free-text "fragmented arguments tool call" and "tool call
streaming assembly" — and `git log` over both named files. (The host API began returning
rate-limit errors partway through; the searches above completed before that and the timeline
cross-reference query did not. I note the gap rather than presenting the survey as
exhaustive.)
Nothing open or merged implements this:
- **#7114** (MERGED 2026-03-11) introduced `streaming_tool_dispatch_events` and the whole
dispatch/reasoning SSE feature. It is the origin of the same-chunk assumption.
- **#12680** (MERGED 2026-08-12) scoped the dedup key per choice for `n>1`. That is the
`(choice.index, id)` HashSet on `main` today — a narrower fix to the same function, and the
reason regression case 8 exists.
- **#8582** (MERGED 2026-04-24) added `merge_tool_call_chunk` for #8640, on the non-streaming
aggregation path only. The streaming dispatcher was not touched.
- **#6845** ("feat(llm): early tool-call completion via streaming args tracker") is CLOSED
and unmerged, branch `feature/streaming-tool-calls`. It is the prior art the issue says to
mine for design and explicitly *not* to cherry-pick: its scanner keyed state only when id
and name coexisted, recognized only `{`/`}`, never parsed the result, and clamped a leading
`}` such that `}{"x":1}` read as structurally complete.
- **#10985** ("fix(llm): preserve fragmented agent tool calls") is CLOSED and unmerged.
- **#10988** and **#11045** (both MERGED) address fragmented tool calls in the *parser* layer
(publish on finish, synthesize `tool_calls` finish reason), not the dispatch extension.
- **#13821** is an OPEN **issue**, not a PR — the referenced Python-side change has not
landed, which is what makes fixing the Rust side ahead of it worthwhile rather than urgent
firefighting.
Recent `git log` over `openai.rs` shows sustained active maintenance of this file
(`#13930` typed v1 jail errors, `#13359` scope tool parsing to request semantics, `#12201`
enforce `parallel_tool_calls: false`, `#12680`, `#12639` emit role once). Over
`aggregator.rs`, `#13730` (preserve nvext through tool-call jail, MERGED 2026-08-27) is the
most recent. The direction of travel is toward stricter, better-scoped tool-call semantics in
these two files — this change is with the grain, not against it.
There is no open PR to help land instead of competing with. `Route: implementation` stands,
and there is no `Disposition: already-resolved`.
### Documentation target
Grepping `docs/` for `tool_call_dispatch` and `enable-streaming-tool-dispatch` returns two
files. `docs/fern/pages/blog/2026/agentic-harness-support.mdx` is the real target: its
"Streaming Tool Calls" section carries the table row "Dispatch | typed `event:
tool_call_dispatch` side channel | at the same structural completion point, but already
parsed" and the sentence "That event tells the harness, in one shot, that the tool call is
ready to execute. No harness-side delta assembly, no guessing whether the arguments are
complete, and no custom parser living inside the harness." That claim is currently *false* for
fragmented streams and becomes true after this change — the issue asks that it remain true,
which means the surrounding text must state the actual convention (Dynamo assembles the
fragments and JSON-syntax-validates the complete argument string; the client still owns
schema validation and execution policy). The other hit,
`docs/fern/pages/reference/general/releases/dynamo-v1-2-0.mdx:332`, is a historical release
note describing #7561 and must not be retroactively edited.
The CLI help text at `components/src/dynamo/frontend/frontend_args.py:545-559` says the flag
emits an event "for each complete tool call before finish_reason arrives", which stays
accurate but is worth a precision pass now that "complete" acquires a defined meaning.
## Chosen approach
Replace the same-chunk detector with a request-local assembly state machine, built on the
merge policy that already exists rather than a second one.
**1. Extract one merge policy, do not write a third.** Move `merge_tool_call_chunk` (and its
doc comment lineage to #8640) out of `aggregator.rs` into a shared, crate-visible home under
`lib/llm/src/protocols/openai/chat_completions/`, and give it a return value describing the
merge outcome — success versus an identity conflict naming the offending field. The
aggregator's one call site at aggregator.rs:414 keeps ignoring the outcome, so #8582/#8640
behavior is bit-for-bit preserved; the dispatcher acts on it and fails closed. I chose
extraction over parity-testing two implementations because the two consumers already share
the accumulator *type* (`ChatCompletionMessageToolCallChunk`), so there is nothing to
translate, and because parity tests decay: they prove agreement at the moment they are
written and quietly stop covering the next field somebody adds.
**2. Request-local assembly state keyed by `(choice.index, tool_call_chunk.index)`.** Declared
beside `reasoning_buffer` in the per-request streaming branch (openai.rs:2935-2941), replacing
`dispatched_tool_ids`. Each live entry holds an accumulated
`ChatCompletionMessageToolCallChunk`, incremental scanner state, and a status
(`Accumulating` / `Invalid` / `Emitted` tombstone). An entry is created for *every* tool-call
chunk, with no requirement that id and name coexist — that requirement is precisely #6845's
mistake. Arguments arriving before identity is legal and dispatches later. Because the key is
the pair, two choices reusing inner index 0 and the same call ID cannot collide (case 8) and
two calls in one choice at inner indexes 0 and 1 can interleave and complete out of order
(case 7). The tombstone, not a separate ID set, gives exactly-once emission and keeps
`test_tool_dispatch_dedup_skips_already_dispatched_id` (case 11) green.
**3. An incremental O(n) JSON structural scanner.** Per entry, carry container-depth,
in-string, and pending-escape state across fragment boundaries, so quoted braces, escaped
quotes, and a backslash split across two chunks never create a false boundary (case 5). Scan
only the bytes of the arriving fragment — never re-parse the accumulated buffer — because
`serde_json::from_str` on the whole buffer per token is quadratic in exactly the long-argument
case #13821 makes common. Recognize self-delimiting top-level objects *and* arrays, including
nested mixed containers. A closing token when depth is zero is a structural error that marks
the entry `Invalid` rather than clamping to zero — that single decision is what makes
`}{"x":1}` a permanent non-dispatch and is the named regression against #6845's scanner. The
entire current fragment is consumed before a candidate is declared, so `{}junk` never
dispatches at the first `}` (case 6). Only when the root container closes and the fragment
remainder is whitespace does `serde_json::from_str` run once over the accumulated string;
structural scanning proposes, `serde_json` confirms. Emission additionally requires id and
name to be present. A top-level scalar is not a candidate for early dispatch — `1` may still
receive `2` — and waits for the terminal pass. After a successful emission, a later
non-whitespace continuation for that key is a producer violation: log and suppress, since an
emitted SSE event cannot be retracted.
**4. A terminal completion pass.** On `finish_reason: "tool_calls"` for a choice, walk that
choice's live entries once. Valid accumulated JSON emits; absent or empty-string arguments
emit under the existing parameterless-tool compatibility rule — this is the only safe place
for it, because the choice has definitively stopped producing; non-empty invalid JSON does
not emit and is logged. The accumulated argument string is emitted verbatim, never rewritten.
On any other terminal condition — `length`, backend error, disconnect, raw EOF — unfinished
state is cleared without emitting; nothing valid is lost there, because a syntactically
complete call would already have dispatched early. Tombstones outlive the clearing of
unfinished state for the life of the request; the whole structure dies with the HTTP stream.
**5. Placement stays exactly where it is.** The loop order at openai.rs:2947-3025 already
matches the issue's section 4, so the change is confined to what happens *inside* the
dispatch call plus a terminal hook on the same call. `parallel_tool_calls=false` filtering
continues to run first, so a filtered higher-index call is never even accumulated (case 9).
The dispatcher continues to observe rather than consume: it must not rewrite, duplicate, or
re-aggregate the standard deltas, and the response still passes once through `EventConverter`,
metrics, and response collection. The payload keeps borrowing a
`ChatCompletionMessageToolCallChunk` — now from the state entry — so the wire format is
untouched, no synthetic ordinary chunk is ever produced, and the extension stays opt-in.
**6. Tests and helpers.** Give `make_choice_with_tool_call` an explicit inner tool-call index
parameter so cases 7 and 9 are expressible, and update its existing call sites. For
quoted-brace payloads, assert against typed state or real SSE serialization rather than
`extract_sse_data_json`, whose brace-only scan would fail inside the helper. Case 12 — the
stream-level proof that every ordinary fragment stays an ordinary `data:` event and that
exactly one dispatch event precedes the fragment completing the JSON — is the test that
justifies the whole change and should assert on ordering, not merely on presence. Do not
re-add coverage the file already has (the single-chunk happy path, the `n>1` choice-index
case, the missing-id/name cases); do change
`test_tool_dispatch_empty_arguments_still_dispatches`, since `Some("")` deliberately stops
dispatching early and becomes a terminal-pass assertion instead.
**7. Documentation.** Update the "Streaming Tool Calls" section of
`docs/fern/pages/blog/2026/agentic-harness-support.mdx` to state the real completion
convention, keeping the "no harness-side delta assembly" promise true, and adding that JSON
closure is a Dynamo early-dispatch convention rather than something the OpenAI protocol
supplies, and that syntax validity is not schema validity. Leave the v1.2.0 release note
alone. Optionally tighten the flag help text in
`components/src/dynamo/frontend/frontend_args.py`.
### On optional versus required parameters
The plan threads new request-local state through `streaming_tool_dispatch_events`, so the
question of whether callers must change is live. I checked the call graphs rather than
guessing: `streaming_tool_dispatch_events` is a private free function with exactly two
callers, the handler at openai.rs:2991 and the test helper at openai.rs:7743, both inside
`lib/llm/src/http/service/openai.rs`. `merge_tool_call_chunk` is private with exactly one
caller, aggregator.rs:414. Nothing outside `dynamo-llm` reaches either.
Given that, I chose **required** parameters for the dispatcher: replace the
`&mut HashSet<(u32, String)>` with `&mut` the new assembly state outright, and take the
terminal-pass trigger from the response the function already receives rather than adding an
`Option`. Making it optional would buy nothing — there is no third caller to spare — and
would leave a permanently-`None` branch that the tests would have to keep alive. The one
place I chose the **additive** shape is the shared merge helper: raising its visibility and
adding a return value leaves the aggregator's call site compiling unchanged, whereas
restructuring it into a trait or a new type would ripple into code that has no stake in this
fix. If a conflict outcome later needs richer structure, that is an additive change to a
`pub(crate)` enum, not a signature break.
`cargo check --workspace --all-targets` from Recipe 2, plus the separate
`--manifest-path lib/bindings/python/Cargo.toml` pass (that crate has its own workspace and
is not covered by the root one), is the evidence that I found every caller — not this
paragraph. Recipe 2's own history is the argument: #12146 passed a per-crate build and failed
CI two minutes later on two callers in crates nobody had built.
## Rejected alternatives
**Write a second merge routine local to the dispatcher.** Fastest to land and needs no
aggregator edit, but the issue forbids it by name, and for a good reason: two field-merge
policies over the same wire type will drift the first time a field is added, and the drift
will be invisible until a harness executes a wrong tool call. Rejected.
**Keep `merge_tool_call_chunk` private and prove parity with tests.** The issue offers this as
the fallback. Rejected because the two consumers share the accumulator type outright, so there
is no impedance to justify duplication, and because parity tests only assert agreement at the
moment of writing.
**Add conflict detection inside the aggregator's merge behavior.** Tempting — a conflicting
identity is a producer bug on both paths — but it would change #8582/#8640's shipped
behavior on the non-streaming path, which this issue does not ask for and which has its own
regression tests. Reporting the conflict and letting each consumer decide keeps one policy
without changing the aggregator's observable behavior. Rejected as scope creep in its
behavior-changing form; adopted in its report-only form.
**Cherry-pick #6845's scanner.** Rejected, and the issue is explicit about why. Its four
defects map one-to-one onto four of the twelve regression cases: id-and-name-together state
initialization (case 4), object-braces-only recognition (case 5's array and nested-container
half), never parsing the result (case 6's truncated-JSON half), and depth-clamping such that
`}{"x":1}` reads complete (case 6's mismatched-container half). The new tests must reject that
input specifically.
**Re-parse the whole accumulated buffer with `serde_json` after each fragment.** Simple and
obviously correct, and rejected on cost: it is O(n²) in total argument bytes, and the long
arguments #13821 restores are exactly the case that motivates the fix. Structural scanning
identifies candidates in O(n); `serde_json` confirms once per candidate.
**Dispatch on `finish_reason` only, dropping early dispatch.** This would be trivially safe
and would delete the feature. The whole point of `tool_call_dispatch` is that the harness
learns it must act before stream end; the blog documents that as the headline benefit.
Rejected.
**Move dispatch to a stream adapter or a new event name.** #6845's shape. Rejected: the issue
names the current `tool_call_dispatch` boundary in the HTTP loop as the correct integration
point, and renaming the event would break existing extension clients.
**Treat `Some("")` as dispatchable early, preserving today's behavior exactly.** Rejected —
it is the first of the three enumerated failure modes. `Some("")` is genuinely ambiguous
mid-stream, and the terminal pass is where it can be resolved safely.
## Validation strategy
This is a Rust change in `dynamo-llm` (`lib/llm/src/http/service/openai.rs` plus a shared
merge helper under `lib/llm/src/protocols/openai/chat_completions/`), a Fern `.mdx` docs
edit, and possibly one Python help string. The load-bearing evidence is Recipe 2: the new
state machine and its scanner are pure, deterministic, and fully exercisable by
`cargo test -p dynamo-llm --lib`, which is where all twelve regression cases will live
alongside the existing dispatch tests at openai.rs:7808-8090.
**Recipe 2 — rust-cargo-check.** The primary evidence. Section 1 (`git diff --check`,
`cargo fmt --all --check`) catches formatting before a long build. Section 2 is
`cargo check --workspace --all-targets` plus the separate
`--manifest-path lib/bindings/python/Cargo.toml` pass; `--all-targets` matters here because
the changed function's second caller lives in a `#[cfg(test)]` block, and `--workspace` is
what proves the merge-helper move did not orphan a caller in a crate nobody opened. Section 3
is `cargo clippy --workspace --all-targets --no-deps -- -D warnings` — worth attention on a
byte-scanning loop, which attracts `needless_range_loop` and manual-`memchr` style lints.
Section 4 is `cargo test -p dynamo-llm --lib`, the run that must show the new regression cases
passing and — critically — the pre-existing aggregator tests
(`test_issue_8640_split_tool_call_arguments_reconstructed`,
`test_parallel_tool_calls_interleaved_chunks_aggregate_independently`,
`test_parallel_tool_calls_false_caps_to_first_call`) still green, which is what proves the
merge-helper extraction did not disturb the non-streaming path. No GPU, no CUDA, no Docker.
A note on making the evidence non-tautological: for the three enumerated failure modes, the
new tests should be written so they fail against the current predicate. An identity opener
followed by argument-only fragments emits nothing today (mode 2) and must emit exactly one
complete event after; a truncated prefix dispatches today (mode 3) and must not; `Some("")`
followed by real fragments dispatches an empty call today (mode 1) and must not. If a new
test passes on unmodified `main`, it is not testing the fix. The validator should record the
pre-change failure where practical, per the template's validator focus.
**Recipe 1 — python-lint.** The docs `.mdx` edit and any `frontend_args.py` help-text change
go through Section 2's `pre-commit run --files ... --hook-stage manual`, which is where the
repo's Fern frontmatter, SPDX, and codespell rules are enforced — and where a documentation
edit most often fails. Section 1 is N/A if no Python file ends up touched.
**Recipe 0 — dynamo-editable-install.** Mandatory preflight for Recipe 7, which imports
`dynamo.*`. `compute-env.md` reports `dynamo._core` was already built by pre-agency
preparation, so this is the idempotent confirmation rather than a rebuild.
**Recipe 7 — vLLM aggregate smoke.** Engine is `vllm`, matching `$GLAMR_CODING_ENGINE` and
the baked-in vLLM 0.26.0; one A100-SXM4-80GB is attached, and the recipe uses Qwen3-0.6B with
`--load-format dummy`, so there is no weight download. I nominate it because the change edits
the live HTTP handler that serves *every* streaming chat completion, not an isolated library
function: the printer will restructure state ownership inside the `async_stream::stream!`
loop and add a terminal hook, and that is exactly the class of change that can break the real
handler while unit tests of the extracted function stay green. Section 2's functional request
should be issued twice — once as written, and once with `"stream": true` — so the SSE path
itself is exercised end to end and the ordinary `data:` frames are observed unchanged, which
is the process-level companion to regression case 12. Section 3's teardown assertion (clean
exit, card back to baseline, zero ERROR/Exception lines) is the no-regression signal.
Its limit, stated up front so nobody over-reads it: with `--load-format dummy` the model
emits garbage tokens and will never produce a real tool call, so Recipe 7 cannot prove
dispatch behavior. It is a no-regression control on the shared streaming path. All positive,
malformed-input, and boundary evidence for the state machine comes from Recipe 2 Section 4.
Not nominated, with reasons: Recipe 5 (code-inspection) — everything here executes locally,
and inspection is the fallback for what the sandbox cannot run. Recipe 8 (disagg-pair-smoke) —
nothing in this change touches KV transfer, routing, NIXL, or worker lifecycle; the HTTP
frontend behaves identically under aggregated and disaggregated backends. Recipe 3
(python-unit-tests-mocker) — no Python logic changes. Recipe 6 (dockerfile-build) — no
Dockerfile touched, and no Docker socket in this sandbox. Recipe 9 (gpu-pytest) — no
GPU-dependent pytest covers the dispatch extension. Recipe 10 (perf-benchmark) — the O(n)
scanner is an *avoidance* of a quadratic cost that does not exist on `main` today, not a
performance claim about the shipped path; asymptotic reasoning plus Recipe 2 is the honest
evidence, and a benchmark here would measure noise. Recipes 11-17 — wrong language, wrong
layer, or wrong engine.
```validation-recipes
00-dynamo-editable-install
01-python-lint
02-rust-cargo-check
07-agg-smoke
```
## Required deliverables
The standard agency packet set for this template, in order:
- `plan.md` — this file.
- `change.md` and `change.diff` — the printer's committed Rust correction: the shared merge
helper with conflict reporting, the request-local assembly state machine and incremental
JSON scanner in `streaming_tool_dispatch_events`, the terminal completion pass, the
`make_choice_with_tool_call` index parameter, the twelve regression cases including the
stream-level ordering test, and the `agentic-harness-support.mdx` documentation update.
Commits are local and signed off (`git commit --signoff`) on `fix/issue-13972--d54bf171860b`
off `main`; the printer does not publish.
- `change-validation.md` — the validator's recorded runs for recipes 00, 01, 02, and 07,
each through the recorder, ending in exactly one of `## Verdict: pass`, `fail`, or
`blocked`. Recipe 2 Section 4 is the section that must carry the regression evidence, with
the pre-change failure recorded where practical.
- `review.md` — the reviewer's assessment that the tests fail for the old behavior, that
malformed and truncated input never dispatches, that `}{"x":1}` is rejected, that the
aggregator's non-streaming path did not regress, and that the ordinary OpenAI stream is
byte-for-byte unchanged. Ends in exactly `## Assessment: sound` or `needs_changes`.
- The publisher alone pushes the branch and opens the pull request against `main`, with a
description carrying the issue URL, `## Summary`, and `## Validation`, then watches CI to
completion. Full CI on this repository runs only after a maintainer comments
`/ok to test <sha>`; that is a human gate outside our control and should be stated in the
handoff rather than waited on indefinitely. |
Collaborator
Author
change.md# Change — ai-dynamo/dynamo#13972: fix `tool_call_dispatch` argument reconstruction
Branch: `fix/issue-13972--d54bf171860b`
Base: `main`, merge-base `b4338ab87`
HEAD: **`da2835a06`**
Working tree: clean.
Four commits on the branch, all signed off. Iteration 1's commit was not amended or rewritten.
| Commit | Subject |
|---|---|
| `4e17a9f2c` | `refactor(llm): extract shared tool-call chunk merge policy` *(iteration 1)* |
| `938ceeabc` | `fix(llm): correct the tool-call merge seam's conflict reporting` |
| `6e2550bbc` | `fix(frontend): assemble fragmented tool-call arguments before dispatch` |
| `da2835a06` | `docs: describe tool_call_dispatch assembly and completion rules` |
## Does the branch fix #13972 now?
**Yes.** Iteration 1 landed groundwork only and said so. This iteration landed plan steps 2, 3, 4,
6, and 7: `lib/llm/src/http/service/openai.rs` no longer decides tool-call completeness from a
single delta chunk, and `dispatched_tool_ids: HashSet<(u32, String)>` and the `has_name_and_args`
predicate are both gone. The reported defect — a `tool_call_dispatch` event carrying a truncated
argument prefix such as `{"path":"/a/very`, followed by permanent suppression of that call through
the `(choice_index, id)` dedup set — is closed, and there are tests that fail without the fix (see
[Non-tautology evidence](#non-tautology-evidence)).
One honest caveat carried forward: this is validated by unit tests and the three named gates only.
No engine-in-the-loop run against a real vLLM/SGLang hermes producer was performed, so the claim
that the new completion rules match live producer emission rests on the delta shapes described in
the issue and the OpenAI streaming spec, not on observed traffic.
## Requested change 1 — rustfmt `max_width`
Fixed in `938ceeabc`. The 101-character line at the old `tool_call_merge.rs:161` was wrapped by
`cargo fmt` itself rather than by hand. `cargo fmt --all --check` now exits 0 (verbatim result
below); the failure iteration 1 reported is gone and did not recur across the two later commits.
## Requested change 2 — `ToolCallIdentityField::as_str` dead code
Answered the reviewer's **first-preference** way: the reporting surface now has the caller it was
built for, so nothing is suppressed.
`938ceeabc` carried an interim `#[allow(dead_code)]` with a `TODO` naming the state machine as the
removal condition, purely so the branch was gate-clean at that point in case work stopped there
(the task asked for incremental commits that each survive on their own). `6e2550bbc` **deleted**
that `allow` and its `TODO`, because `update_tool_call_assembly` now calls `field.as_str()` in its
fail-closed `tracing::warn!`. There is no `#[allow(dead_code)]` anywhere on the branch, and
`cargo clippy --workspace --all-targets --no-deps -- -D warnings` exits 0.
## Requested change 3 — asymmetric empty guard on `id` / `function.name`
Fixed in `938ceeabc`, **report-only**. The `id` and `function.name` conflict arms now require both
sides to be non-empty:
```rust
(Some(current), Some(id)) if !current.is_empty() && !id.is_empty() && *current != id => {
note(ToolCallIdentityField::Id)
}
```
Previously only the *incoming* value was checked, so a producer opening with `id: ""` and carrying
the real value in a later delta was reported as a conflict while the mirrored ordering was
correctly treated as a no-op.
**No mutation site changed.** The guard lives entirely inside the `note(...)` arm, which only
records a field name; `existing.id` is still assigned in exactly one place, the `(None, Some(id))`
arm, and `function.arguments` is still unconditionally `push_str`-ed. The aggregator's observable
behavior is bit-for-bit identical — the aggregator discards the outcome, so the only thing the
guard can change is a value nothing there reads.
The requested test landed as `empty_established_identity_value_is_not_a_conflict`
(`tool_call_merge.rs`): accumulator established with `Some("")` for `id` and `name`, then a chunk
with `Some("call-1")` / `Some("calculator")`; asserts `Merged` and that the accumulator is
unchanged (`id == Some("")`, `name == Some("")`).
## Requested change 4 — forward-compat-only `r#type` arm
Fixed in `938ceeabc`. The arm now carries an in-place comment saying it cannot fire today because
`FunctionType` has exactly one variant in the OpenAI schema, and that it is kept so a second
variant cannot silently acquire unreported first-wins semantics. `ToolCallIdentityField::Type` is
therefore unreachable in practice by design, not by oversight.
## Requested change 5 — stale bare mention at `aggregator.rs:251`
Fixed in `938ceeabc`. The `//` comment inside `finalize_merged_tool_chunk` now points at the
sibling module rather than naming a function that no longer lives in that file.
## The fix — `lib/llm/src/http/service/openai.rs` (+952 / −83)
### Assembly state (plan step 2)
`streaming_tool_dispatch_events` no longer takes `dispatched_tool_ids: &mut HashSet<(u32, String)>`.
It takes `&mut ToolCallAssemblies`, a `HashMap<(u32, u32), ToolCallAssembly>` keyed by
`(choice.index, tool_call_chunk.index)` — the tool call's *own* inner index, not its `id`, which is
what makes assembly work before an `id` has arrived. The map is created inside the
`async_stream::stream!` branch, so it is request-local and dies with the HTTP stream.
Each entry holds the merged `ChatCompletionMessageToolCallChunk`, a scanner, an `AssemblyState`
(`Accumulating` / `Invalid` / `Emitted`), and a `json_confirmed` flag. Merging reuses
`merge_tool_call_chunk` from the extracted module, so the side channel and the non-streaming
aggregator cannot disagree about the same call. An `IdentityConflict` logs the field name
(`as_str()`) and marks the entry `Invalid` — fail closed. `Emitted` is a tombstone: a later chunk
for an already-emitted key is ignored, and warns only if it is not an exact replay.
### Incremental JSON scanner (plan step 3)
`JsonStructureScanner` carries `depth`, `in_string`, `pending_escape`, `root_started`,
`scalar_root`, `root_closed`, and `malformed` across fragment boundaries, so every byte is examined
once — O(n) over the whole argument string rather than an O(n²) re-parse per fragment. `serde_json`
confirms the value exactly once, at the first candidate boundary; the scanner decides *when* to
ask, `serde_json` decides *whether* it is valid.
The rules that matter for the named cases:
- A `}` or `]` as the first non-whitespace byte, or at depth zero, is permanently `Malformed`. This
is what makes `}{"x":1}` a permanent non-dispatch — the failure mode of the depth-clamping
scanner in closed PR #6845.
- Any non-whitespace byte after the root closes is permanently `Malformed`, which covers `{}junk`
and `{}{}`.
- A first non-whitespace byte that is neither `{` nor `[` sets `scalar_root`: leading junk and
top-level scalars are never early candidates and are left to the terminal pass.
- `"` toggles string state and `\` sets `pending_escape`, so braces inside string literals and
escaped quotes do not close the value early.
### Terminal pass (plan step 4)
`finalize_choice_assemblies` runs on `finish_reason`. Keys are sorted before iteration because
`HashMap` order is unstable and the emitted event order must not be. A non-`ToolCalls` finish
reason drops every still-`Accumulating` assembly without emitting. Under `ToolCalls`, absent or
empty `arguments` are treated as usable — the parameterless-tool compatibility rule — and anything
else must be valid JSON, re-checked only if the scanner never confirmed it. Assemblies without
identity are dropped rather than emitted.
Ordinary SSE frames are untouched throughout; the dispatch event is pushed before the ordinary
frame that completes the JSON.
## Tests (plan step 6)
`make_choice_with_tool_call` gained the inner-index parameter and now delegates to a new
`make_choice_with_tool_calls`, alongside helpers `tool_call_chunk`, `make_finish_choice`,
`drive_to_tool_calls_finish`, `feed_fragments`, `assembled_arguments`, and `scan_all`.
Sixteen `test_13972_*` cases plus `test_json_scanner_boundaries`:
| Test | What it pins |
|---|---|
| `test_13972_identity_opener_then_argument_fragments` | the canonical hermes shape: exactly one dispatch, on the closing fragment |
| `test_13972_truncated_prefix_never_dispatches` | `{"path":"/a/very` never dispatches, at any point |
| `test_13972_empty_opener_then_fragments_does_not_dispatch_early` | `Some("")` opener does not dispatch early; real fragments still assemble |
| `test_13972_identity_after_arguments_still_assembles` | arguments may precede identity |
| `test_13972_conflicting_identity_fails_closed` | disagreeing `id` across chunks → no dispatch |
| `test_13972_quoted_and_escaped_braces_do_not_close_early` | `}` inside a string, and `\"`, do not close the root |
| `test_13972_nested_and_array_roots_complete` | nested objects and array roots |
| `test_13972_trailing_junk_never_dispatches` | `{}junk` |
| `test_13972_mismatched_containers_never_dispatch` | `}{"x":1}` — permanent, per PR #6845 |
| `test_13972_leading_junk_never_dispatches` | leading non-container bytes |
| `test_13972_canonical_empty_object_dispatches_early` | `{}` dispatches at the scanner, not the terminal pass |
| `test_13972_interleaved_inner_indexes_complete_out_of_order` | parallel calls interleaved, completing out of order |
| `test_13972_same_id_and_inner_index_across_choices_do_not_collide` | keying includes `choice.index` |
| `test_13972_filtered_higher_index_call_is_never_accumulated` | no entry is created for a call the response never carries |
| `test_13972_terminal_pass_outcomes` | empty/absent args emit at terminal; incomplete JSON and non-`ToolCalls` finish do not |
| `test_13972_dispatch_event_precedes_the_completing_fragment` | exact wire order `["data:0", "data:1", "data:2", "tool_call_dispatch", "data:3"]` |
| `test_json_scanner_boundaries` | scanner outcomes directly, at fragment boundaries |
`test_tool_dispatch_empty_arguments_still_dispatches` was renamed to
`test_tool_dispatch_empty_arguments_dispatch_at_terminal_pass` and now asserts the event arrives
only after the terminator — the same call still dispatches, but later and for a stated reason.
## Non-tautology evidence
Two proofs were run, one per commit that changed behavior.
**Requested change 3.** Reverting the symmetric guard in `merge_tool_call_chunk` (restoring the
one-sided `!id.is_empty()` check) made `empty_established_identity_value_is_not_a_conflict` fail:
```
assertion `left == right` failed
left: IdentityConflict { field: Id }
right: Merged
```
**The dispatcher fix.** Rather than `git stash` (which would have removed the new tests along with
the fix), I patched `update_tool_call_assembly` in place to restore `main`'s decision policy —
dispatch as soon as one chunk carries `id` plus `function.name` plus `function.arguments` — while
keeping the new tests and the key/type shell so they still compile. That isolates the completion
policy, which is the thing under test.
```
cargo test -p dynamo-llm --lib -- _13972
test result: FAILED. 3 passed; 13 failed
```
All three cases the task named as required failures were among them:
- `test_13972_empty_opener_then_fragments_does_not_dispatch_early` — FAILED
- `test_13972_identity_opener_then_argument_fragments` — FAILED
(`left: 0, right: 1` — "exactly one dispatch, on the fragment that closes the JSON")
- `test_13972_truncated_prefix_never_dispatches` — FAILED
as was the ordering case, which shows the old path never emitting at all for a fragmented call:
```
assertion `left == right` failed: the dispatch event precedes the ordinary fragment that
completes the JSON, and every ordinary fragment survives
left: ["data:0", "data:1", "data:2", "data:3"]
right: ["data:0", "data:1", "data:2", "tool_call_dispatch", "data:3"]
```
The three that passed under the reverted policy are the ones that do not depend on it:
`test_13972_canonical_empty_object_dispatches_early`, `test_13972_nested_and_array_roots_complete`,
and `test_13972_filtered_higher_index_call_is_never_accumulated`. The file was then restored from a
byte-identical copy taken before the patch, and the suite re-run to 16/16 green before committing.
The temporary revert was never committed.
## Gate results
Run from the checkout at `da2835a06`, working tree clean.
| Command | rc | Tail |
|---|---|---|
| `cargo fmt --all --check` | **0** | no output |
| `cargo clippy --workspace --all-targets --no-deps -- -D warnings` | **0** | ``Finished `dev` profile [unoptimized + debuginfo] target(s) in 32.19s`` |
| `cargo test -p dynamo-llm --lib` | **0** | `test result: ok. 2451 passed; 0 failed; 5 ignored; 0 measured; 0 filtered out; finished in 8.10s` |
The three pre-existing aggregator regressions the task named, run by name:
```
test protocols::openai::chat_completions::aggregator::tests::test_issue_8640_split_tool_call_arguments_reconstructed ... ok
test protocols::openai::chat_completions::aggregator::tests::test_parallel_tool_calls_interleaved_chunks_aggregate_independently ... ok
test protocols::openai::chat_completions::aggregator::tests::test_parallel_tool_calls_false_caps_to_first_call ... ok
test result: ok. 3 passed; 0 failed; 0 ignored; 0 measured; 2453 filtered out
```
Two extra checks beyond the required three, since the repository's pre-commit config has no Rust
hook and would not catch a recurrence:
| Command | rc |
|---|---|
| `cargo clippy --manifest-path lib/bindings/python/Cargo.toml --all-targets --no-deps -- -D warnings` | **0** |
| `pre-commit run --files <the three changed files>` | **0** — all applicable hooks passed, the rest skipped |
`rustfmt` and `clippy` components were added to the 1.93.1 toolchain with `rustup component add`
in iteration 1; that remains the only environment intervention.
## Documentation (plan step 7)
`docs/fern/pages/blog/2026/agentic-harness-support.mdx`, "Streaming Tool Calls" (+2 lines, one
paragraph). The section already claimed the dispatch event means "no harness-side delta assembly,
no guessing whether the arguments are complete" — a claim the old code did not support. The new
paragraph states the rules that now back it: per-request assembly keyed by choice index and
tool-call index, incremental JSON completion with `}`-inside-a-string called out, the
parameterless-tool case resolving at `finish_reason`, at-most-once emission, and fail-closed
behavior falling back to the ordinary tool-call deltas. `dynamo-v1-2-0.mdx` was left alone.
## What did not get done, and residual risk
- **No live-engine validation.** Unit tests only. Nobody ran a real hermes-emitting producer
against this.
- **No integration or Python-level test.** The dispatch path is exercised only through the Rust
unit tests in `openai.rs`; `pytest` was not run.
- **Behavior change for consumers already relying on the old timing.** A harness that today
receives a dispatch event on the opening chunk will now receive it later — at JSON completion or
at `finish_reason` — and, for a call whose arguments never become valid JSON, not at all. That is
the point of the fix, but it is a behavior change on an opt-in feature and should be called out
in the PR description. The ordinary tool-call deltas are unchanged in all cases, so nothing is
lost, only re-timed.
- **`ToolCallIdentityField::Type` is still unreachable.** Documented as forward-compat, per
requested change 4; no test covers it because no input can produce it.
- **`Copy`-ing `finish_reason`** relies on `FinishReason` being `Copy`, which it is today via the
`async_openai` re-export. If that ever changes, the terminal pass will need a `clone`.
- **Scanner is structural, not a validator.** It decides *when* to hand a candidate to
`serde_json`; malformed-but-balanced input such as `{,}` is rejected by `serde_json`, not by the
scanner. That is deliberate, but it means the scanner's `RootClosed` must never be read as
"valid JSON" on its own.
## Files
| File | Delta | Note |
|---|---|---|
| `lib/llm/src/http/service/openai.rs` | +952 / −83 | the fix: assembly state, scanner, terminal pass, 17 new tests |
| `lib/llm/src/protocols/openai/chat_completions/tool_call_merge.rs` | +222 (new) | extracted merge policy, 5 tests; `#[allow(dead_code)]` added then removed |
| `lib/llm/src/protocols/openai/chat_completions/aggregator.rs` | +8 / −52 | function moved out; two comments repointed |
| `lib/llm/src/protocols/openai/chat_completions.rs` | +1 | module declaration |
| `docs/fern/pages/blog/2026/agentic-harness-support.mdx` | +2 | completion rules paragraph |
`change.diff` is `git diff b4338ab87..HEAD` and covers all four commits.
MR URL: https://github.com/ai-dynamo/dynamo/pull/13986 |
Collaborator
Author
change-validation.md# Change validation — ai-dynamo/dynamo#13972, commit `da2835a06`
Branch `fix/issue-13972--d54bf171860b`, HEAD
`da2835a0649685356893fb602b70f3e980a1e5f5`, three commits ahead of merge-base
`b4338ab87`. The working tree was clean when I started and is clean now
(`git status --porcelain` empty, HEAD unchanged). I added no commits, staged
nothing, and made no edit to make a gate pass. One temporary, deliberately
*breaking* edit was made for the non-tautology experiment below and restored
byte-identically; it is disclosed in full.
Iteration 2 differs from iteration 1 in a way that matters for reading this
packet: the printer has landed plan steps 2–7, so `lib/llm/src/http/service/
openai.rs` — the live SSE streaming handler — is now edited rather than
byte-identical to `main`.
Every command below was executed through `/workflow/agents/customs/evidence.ts
record`. Nothing is transcribed from `change.md` or inherited from the previous
iteration. Log paths are relative to the work-item root.
## Routing
`compute-env.md`: one local A100-SXM4-80GB, CUDA toolkit 13.0, in-sandbox vLLM
0.26.0, no Docker daemon. Local pathway only — no cluster, SSH, or Slurm was
reached for. The plan's ```validation-recipes``` fence names four recipes:
`00-dynamo-editable-install`, `01-python-lint`, `02-rust-cargo-check`,
`07-agg-smoke`. All four were run. The plan names Recipe 2 as the load-bearing
evidence and Recipe 7 as a no-regression control that, in its own words,
"cannot prove dispatch behavior".
Environment note carried forward and re-confirmed: the sandbox exports
`RUSTUP_TOOLCHAIN=1.93.1`, which **overrides** the repo's `rust-toolchain.toml`
pin of `1.96.1`. Because CI honours the pin and this sandbox does not, both
previously-failing gates were re-run under `1.96.1` as well.
## Evidence [3/4 validated · 1 missing dep]
_Generated from validation/registry.jsonl — do not edit by hand._
| Recipe | Status | Command (deciding run) | Evidence | Note |
|---|---|---|---|---|
| 00-dynamo-editable-install | validated | `dynamo-prepare-python-validation …; python3 -c "import dynamo, dynamo._core"` | `validation/logs/2026-08-28T20-58-28.320Z-bash-67ab.log` | idempotent re-confirmation; env prepared pre-agency |
| 01-python-lint | validated | `pre-commit run --files <5 changed files> --hook-stage manual` | `validation/logs/2026-08-28T21-02-01.063Z-bash-25f2.log` | 0 Python files in the diff; Python-only hooks legitimately skip |
| 02-rust-cargo-check | validated | `cargo fmt --all --check` + `cargo clippy --workspace --all-targets --no-deps -- -D warnings` + `cargo test -p dynamo-llm --lib` | `validation/logs/2026-08-28T21-10-44.421Z-bash-bdb1.log` | load-bearing; per-section logs below |
| 07-agg-smoke | missing dep | `python3 -m dynamo.frontend …` + `python3 -m dynamo.vllm --model Qwen/Qwen3-0.6B --load-format dummy …` | `validation/logs/2026-08-28T21-12-57.252Z-bash-d838.log` | host driver 570.124.06 (CUDA 12.8) vs baked `torch 2.11.0+cu130` (needs CUDA 13.0); engine core cannot start. Re-tested on this HEAD, not assumed. |
The customs report clears at `3/4 validated · 1 missing dep`.
## Scope check, performed before any gate
`git diff --name-status b4338ab87..HEAD` lists exactly five files: an unrelated
`.mdx` blog page, `lib/llm/src/http/service/openai.rs`,
`lib/llm/src/protocols/openai/chat_completions.rs`,
`.../chat_completions/aggregator.rs`, and the new
`.../chat_completions/tool_call_merge.rs`. Zero `.py` files — Recipe 1's Python
sections are N/A by fact, not by omission. The recipe still ran so the SPDX,
whitespace, and markdown hooks were exercised over the changed files; all
applicable hooks reported Passed or Skipped, and `git status --porcelain` was
still empty afterwards (no hook rewrote a file).
## Recipe 2 — per section
**Section 1, formatting.** `git diff --check` rc 0 and `cargo fmt --all
--check` rc 0 on the sandbox default 1.93.1 (rustfmt 1.8.0-stable):
`validation/logs/2026-08-28T20-58-37.987Z-bash-4ba7.log`. Re-run on the pinned
`1.96.1` (rustfmt 1.9.0-stable), the toolchain the review reproduced the failure
on: rc 0, `validation/logs/2026-08-28T20-58-55.216Z-bash-5407.log`. The only
line in `tool_call_merge.rs` wider than 100 columns is line 1, the SPDX header,
which rustfmt does not width-check.
**Section 2, type check.** `cargo check --workspace --all-targets` rc 0
(54.08s); `cargo check --manifest-path lib/bindings/python/Cargo.toml
--all-targets` rc 0 (15.06s):
`validation/logs/2026-08-28T20-59-07.417Z-bash-871d.log`.
**Section 3, lints.** `cargo clippy --workspace --all-targets --no-deps -- -D
warnings` rc 0 (32.19s) plus the bindings workspace rc 0, on 1.93.1:
`validation/logs/2026-08-28T21-01-49.817Z-bash-2cc5.log`. Repeated on the
pinned `1.96.1` (clippy 0.1.96) for `-p dynamo-llm --all-targets`: rc 0,
`validation/logs/2026-08-28T21-06-40.493Z-bash-47c9.log`. There is no
`#[allow(dead_code)]` anywhere in the branch diff, so the lint is cleared by a
real caller rather than suppressed.
**Section 4, tests.**
- Whole crate: `cargo test -p dynamo-llm --lib` → `2451 passed; 0 failed; 5
ignored` — `validation/logs/2026-08-28T21-03-27.347Z-bash-6317.log`, and again
in the final post-restore run `…21-10-44.421Z-bash-bdb1.log`. This matches the
count `change.md` claims.
- The new `#13972` cases: `cargo test -p dynamo-llm --lib -- _13972` → `16
passed; 0 failed`. The plan promised twelve; the printer wrote sixteen, all
named in `validation/logs/2026-08-28T21-05-55.508Z-bash-ab09.log`.
- The three pre-existing aggregator regressions, run **individually by exact
test path** — `test_issue_8640_split_tool_call_arguments_reconstructed`,
`test_parallel_tool_calls_interleaved_chunks_aggregate_independently`,
`test_parallel_tool_calls_false_caps_to_first_call` — each `1 passed; 0
failed`: `validation/logs/2026-08-28T21-06-09.973Z-bash-d693.log`.
Disclosure: an earlier attempt inside `…-bash-ab09.log` passed an invalid
libtest flag and aborted rc 101 three times without running anything. That
attempt proves nothing; it is superseded by the `d693` log and is reported
here rather than dropped.
- The pre-existing dispatch suite plus the scanner unit test: `13 passed; 0
failed`, including `test_json_scanner_boundaries` and the renamed
`test_tool_dispatch_empty_arguments_dispatch_at_terminal_pass` (same `ab09`
log).
- The extracted merge module: `5 passed; 0 failed`, covering both empty-guard
orderings — `validation/logs/2026-08-28T21-06-19.151Z-bash-f8d5.log`.
## Independent non-tautology finding
I did not take the printer's claim on its word.
Method: copy `lib/llm/src/http/service/openai.rs` to a scratch path (sha256
`742d12f010a3c4aea39dff8233d43c1a1ecd4e876846443450364a3eca85fd1c`), then
rewrite the decision policy **inside `update_tool_call_assembly` in place** —
leaving the tests, the assembly map, and `finalize_choice_assemblies` untouched
— back to `main`'s rule, taken verbatim from `git show
b4338ab87:…/openai.rs`: emit as soon as a single chunk carries `id` +
`function.name` + `function.arguments.is_some()`, dedup via the tombstone, no
structural scanning. (`git stash` would have removed the tests too and proved
nothing, which is why the edit was surgical.)
Result — `cargo test -p dynamo-llm --lib -- _13972`:
```
test result: FAILED. 3 passed; 13 failed; 0 ignored; 0 measured; 2440 filtered out
```
`validation/logs/2026-08-28T21-09-14.916Z-bash-481f.log` (recorded exit 101).
This reproduces the printer's claim exactly, including *which* three survive:
`test_13972_canonical_empty_object_dispatches_early`,
`test_13972_nested_and_array_roots_complete`, and
`test_13972_filtered_higher_index_call_is_never_accumulated` — the three whose
expected outcome the old policy happens to reach anyway.
The stronger check: the three cases the **review** named as the ones that must
fail against unmodified `main` are all in the failure list —
- `test_13972_empty_opener_then_fragments_does_not_dispatch_early` (`Some("")`
opener followed by real fragments),
- `test_13972_identity_opener_then_argument_fragments` (identity opener, then
argument-only fragments),
- `test_13972_truncated_prefix_never_dispatches` (the `{"path":"/a/very`
prefix from the issue itself).
The regression tests are therefore load-bearing, not tautological: they fail on
the old decision policy and pass on the new one.
Restoration: the file was copied back and verified byte-identical (sha256
unchanged), `git status --porcelain` empty, HEAD still `da2835a06`. The
post-restore integrity check, `cargo fmt --all --check`, `clippy -D warnings`,
and the full 2451-test suite were then re-run green in a single recorded
command, so the recipe's deciding run reflects the pristine tree:
`validation/logs/2026-08-28T21-10-44.421Z-bash-bdb1.log`. Nothing was
committed.
## The five requested changes in `review.md`
1. **Formatting violation at `tool_call_merge.rs:161`** — **resolved,
empirically.** `cargo fmt --all --check` exits 0 on both 1.93.1 and the
pinned 1.96.1 (Section 1 logs). One of the two gates the review called
blocking.
2. **`dead_code` on `ToolCallMergeOutcome::as_str`** — **resolved,
empirically.** `cargo clippy --workspace --all-targets --no-deps -- -D
warnings` exits 0 on both toolchains (Section 3 logs). The review's preferred
route was taken: `as_str()` now has a real production caller in the step-2
dispatcher at `lib/llm/src/http/service/openai.rs:2884`, inside the
`IdentityConflict` warning. No `#[allow(dead_code)]` was used. The second
blocking gate is cleared.
3. **Symmetric empty-value guard** — **resolved, empirically.** Both the `id`
arm and the `function.name` arm now guard `!current.is_empty() &&
!incoming.is_empty()`. The mutation sites are unchanged, so the arms stay
report-only and the aggregator still keeps the first (empty) value; the
aggregator discards the outcome entirely (`let _ = merge_tool_call_chunk(…)`
at `aggregator.rs:374`). The test the review required exists and passes:
`empty_established_identity_value_is_not_a_conflict` asserts `Merged` **and**
asserts the accumulator still holds `Some("")` for both `id` and
`function.name`. The comment above the arm now states the symmetry the code
actually has. The three pre-existing aggregator regressions passing by name
are the behavioural proof that report-only stayed report-only.
4. **`Type` arm marked forward-compat in place** — **resolved** (source
inspection plus compile). The arm carries an in-place comment stating that
`FunctionType` has exactly one variant in the OpenAI schema today, so the arm
cannot fire and `Type` cannot be reported, and that it is kept so a future
second variant does not silently acquire unreported first-wins semantics. A
comment cannot be proven by a test; clippy at `-D warnings` confirms the
variant is not itself dead.
5. **Stale comment at `aggregator.rs:251`** — **resolved** (source inspection).
Line 252 now names `super::tool_call_merge::merge_tool_call_chunk`, matching
what line 176 already did.
All five are addressed. The two the review called blocking are confirmed by
executed gates, not by reading source.
## Missing evidence, and what it costs
**Recipe 7 (`07-agg-smoke`) is `missing dep`.** I re-ran it on this HEAD rather
than assuming last iteration's result. The worker starts, loads the Qwen3-0.6B
config with `--load-format dummy`, then dies in vLLM 0.26.0 engine-core
startup:
```
WARN compilation_context.__init__: Failed to get device capability: The NVIDIA
driver on your system is too old (found version 12080). …
RuntimeError: Engine core initialization failed. See root cause above.
```
`torch.cuda.is_available()` is `False`; the host driver is 570.124.06 (CUDA
12.8) while the baked wheel is `torch 2.11.0+cu130`, requiring CUDA 13.0.
`/health` stayed at `{"status":"healthy","endpoints":[],"instances":[]}`; no
worker ever registered, so Sections 2 and 3 could not run. This is a property of
the sandbox image versus the host driver, not of the change. The `EXIT` trap
reaped both processes: `nvidia-smi` is back at `1 MiB` used and no `dynamo.*`
processes remain, so nothing leaked and the card is at baseline for the next
run. Recipe 7's own local verdict, per its verdict guidance, is `blocked /
driver-cuda-mismatch`.
The honest cost, stated plainly: **there is no runtime evidence at all for the
streaming path this change edits.** In iteration 1 `openai.rs` was
byte-identical to `main`, so a missing runtime smoke cost nothing. That is no
longer true. This commit rewrites `update_tool_call_assembly`, adds
`finalize_choice_assemblies` on the `finish_reason` path, and changes what the
live SSE handler emits. Everything I proved is in-process unit tests calling
those functions directly. Specifically **not** proven by execution:
- that the real streaming loop wires `finalize_choice_assemblies` into the
terminal chunk correctly, and that the assembly map is genuinely request-local
across concurrent in-flight requests;
- that no `tool_call_dispatch` regression appears against a real engine's
chunking, which differs from the synthetic chunk sequences the tests feed in;
- that ordinary, non-tool streaming still works end to end through the edited
handler.
Even a green Recipe 7 would not have proven the fix — the plan says so, because
`--load-format dummy` emits garbage tokens and never produces a real tool call.
What a green Recipe 7 *would* have supplied is the no-regression assurance in
the third bullet, and that assurance is absent. CI on a driver-matched runner is
the only thing that can supply it. I am not treating unit-test evidence as a
substitute, and a reviewer should weigh this gap rather than read `3/4
validated` as full coverage.
## Verdict: pass |
Collaborator
Author
review.md# Review — ai-dynamo/dynamo#13972, commit `da2835a06`
> 🤖 **Automated AI review — advisory.** An AI agent's judgment of
> whether this change is logically sound on the evidence; not a merge
> authorization. CI, customs, and a human reviewer hold that.
## Assessment: sound
Branch `fix/issue-13972--d54bf171860b`, HEAD `da2835a0649685356893fb602b70f3e980a1e5f5`,
four commits ahead of merge-base `b4338ab87e90fc6edd496879b80ed045c7339967`, working tree
clean, `Signed-off-by` on every commit. The SHA in `change.md` matches the SHA in the clone.
`git diff b4338ab87..HEAD` is byte-identical to `change.diff`.
Iteration 1 implemented step 1 of the plan and nothing else; I assessed it `needs_changes`
with five requested changes. This iteration adds the three commits that actually close the
issue (`938ceeabc` merge-seam corrections, `6e2550bbc` the dispatcher rewrite, `da2835a06`
docs). All five requested changes are resolved, and the change now does what the plan and
the issue ask.
---
## Previous requested changes — per-item disposition
| # | Request | Resolved | Evidence |
|---|---------|----------|----------|
| 1 | rustfmt violation >100 cols at `tool_call_merge.rs:161` | **yes** | The offending test line was reflowed. `awk 'length>100'` over the file reports only line 1 — the 104-char SPDX comment, which rustfmt does not width-check. `cargo fmt --all --check` rc 0 on both the sandbox default toolchain (1.93.1 / rustfmt 1.8.0) and the repo pin (1.96.1 / rustfmt 1.9.0). |
| 2 | `ToolCallIdentityField::as_str` dead code fails `clippy -D warnings` | **yes, via the preferred route** | It has a real production caller: `openai.rs:2884` logs `field = field.as_str()` when a chunk contradicts an established identity. `grep -rn "allow(dead_code)"` over the touched trees returns nothing — the `#[allow]` added in `938ceeabc` was deleted again in `6e2550bbc` once the caller existed. `cargo clippy --workspace --all-targets --no-deps -- -D warnings` rc 0 on both toolchains. |
| 3 | One-sided empty guard misreports a producer no-op as `IdentityConflict` | **yes** | The guards are now symmetric: `tool_call_merge.rs:86` requires `!current.is_empty() && !id.is_empty() && *current != id`, mirrored for `function.name` at `:110-111`. The mutation arms are untouched (`(None, Some(x))` only; `arguments` always `push_str`), so the change stays report-only, exactly as asked. New test `empty_established_identity_value_is_not_a_conflict` (`:198-210`) covers the previously-misreported direction and asserts first-wins is unchanged. |
| 4 | `Type` arm is unreachable — say so in place | **yes** | `tool_call_merge.rs:93-96` now states that `FunctionType` has one variant in the OpenAI schema today, that the arm cannot fire, and why it is kept. |
| 5 | Stale comment at `aggregator.rs:251` still pointing at the deleted local helper | **yes** | Both comment sites (`~:173-175`, `~:248-252`) now name `super::tool_call_merge::merge_tool_call_chunk`, and the call site explains that the outcome is deliberately discarded to preserve #8582/#8640 behaviour. |
---
## Does it close the issue?
I re-read #13972 in full. It indicts three concrete failure modes and specifies the
replacement policy in four numbered sections. Walking them against the code:
**§1 request-local assembly state.** `type ToolCallAssemblies = HashMap<(u32, u32),
ToolCallAssembly>` (`openai.rs:2784`), created per request at `openai.rs:3297` in place of
the old `dispatched_tool_ids: HashSet<(u32, String)>`. `update_tool_call_assembly`
(`:2825`) creates an entry for *every* tool-call chunk — it no longer requires id and name
to coexist on the creating chunk. Merge semantics are the aggregator's, literally: it calls
the extracted `merge_tool_call_chunk`, which is the same function `DeltaAggregator` calls.
That satisfies the issue's "do not introduce a third, subtly different field-merge policy"
directly rather than by parity tests. Identity conflict sets `AssemblyState::Invalid` and
logs (`:2881-2893`). Emission tombstones the key (`AssemblyState::Emitted`, `:2758`), and
the key includes `choice.index`, so two choices sharing an id and inner index cannot
collide.
**§2 early-completion policy.** `JsonStructureScanner` (`:2666-2751`) carries `depth`,
`in_string`, `pending_escape`, `root_started`, `scalar_root`, `root_closed`, `malformed`
across fragment boundaries; `consume` is a single pass over each fragment's bytes, so the
whole scan is O(total argument bytes) as the issue requires. The entire fragment is consumed
before a verdict, so `{}junk` cannot dispatch at the first `}`. A close at depth 0 or as the
first non-whitespace byte sets `malformed` — this is precisely the `}{"x":1}` case #6845 got
wrong, and `malformed` is sticky, so it is a *permanent* non-dispatch, not merely a deferred
one. A first byte that is neither `{` nor `[` sets `scalar_root` and stops scanning, so a
top-level `1` waits for the terminal pass rather than speculating. On `RootClosed` the
accumulated string is confirmed once with `serde_json` and the result cached in
`json_confirmed`, so the confirmation is not repeated. Emission additionally requires
`assembly_has_identity`.
**§3 terminal, empty, malformed.** `Some("")` no longer dispatches on arrival: the empty
opener merges and the scanner sees no root. `"{}"` still dispatches early.
`finalize_choice_assemblies` (`:2936-2999`) runs only on `finish_reason:
Some(FinishReason::ToolCalls)`, treats `None | Some("")` as the parameterless compatibility
case, re-checks `serde_json` otherwise, and drains the choice's keys either way — so
`length`, an error, or an EOF clears state without emitting. The accumulated argument string
is emitted verbatim; nothing rewrites it.
**§4 placement and ordering.** The handler diff is two hunks (`:3297`, `:3352`): the state
variable's type and the argument passed. `streaming_tool_dispatch_events` is still called
after `parallel_tool_calls=false` filtering and `deduplicate_stream_roles`, still before
`EventConverter`, still gated on `if tool_dispatch_enabled`, and still pushes into the same
`events` vec that is drained ahead of the ordinary `data:` event. The response is not
consumed, rewritten, duplicated, or re-aggregated by the tracker.
The three failure modes named in the issue's "Current behavior" section — an
`arguments: Some("")` opener dispatching empty and then being suppressed; an opener with
`arguments: None` never dispatching at all; and a truncated prefix such as `{"path":"/a/very`
dispatching immediately and suppressing the real completion — each now have a named
regression test, and each of those three tests fails when the decision policy is put back.
**Yes, this branch closes #13972.**
The issue's 12-item regression list maps onto the tests one-for-one, including the two the
issue calls out as test-harness hazards: `make_choice_with_tool_call` now takes an explicit
inner tool-call index, and the quoted-brace cases assert on typed state via a new
`assembled_arguments` helper instead of routing a `}`-bearing payload through
`extract_sse_data_json`'s brace-only, string-unaware scan.
---
## The non-tautology proof
The printer and the validator independently patched `update_tool_call_assembly` in place
back to `main`'s decision policy, ran the `_13972` filter, and restored the file. I did not
take this on either agent's word.
The validator's log (`validation/logs/2026-08-28T21-09-14.916Z-bash-481f.log`) records
`test result: FAILED. 3 passed; 13 failed`, naming each failure. The three the plan requires
to fail are all present: `test_13972_empty_opener_then_fragments_does_not_dispatch_early`
(the `Some("")`-then-fragments case), `test_13972_identity_opener_then_argument_fragments`
(the identity opener followed by argument-only fragments), and
`test_13972_truncated_prefix_never_dispatches` (the `{"path":"/a/very` case). The
subsequent log (`…21-10-44.421Z-bash-bdb1.log`) records the post-restore sha256 of
`openai.rs` as `742d12f010a3c4ae…`, matching the hash recorded around the experiment, at
HEAD `da2835a06` with a clean tree. `git status` in my own inspection is clean and
`change.diff` still matches `git diff b4338ab87..HEAD`, so nothing from the experiment
leaked into a commit. I regard the proof as sound.
Three of the sixteen survived the in-place revert
(`filtered_higher_index_call_is_never_accumulated`,
`canonical_empty_object_dispatches_early`, `nested_and_array_roots_complete`). None of them
is a tautology: all sixteen reference `ToolCallAssemblies` and the new inner-index parameter
and therefore cannot compile against unmodified `main` at all, and each of the three still
binds real new behaviour (the first asserts the *absence* of a key in the new state map; the
other two would fail if the scanner rejected `{}`, nested containers, or array roots). The
weakest is `nested_and_array_roots_complete`, whose assertion is a final dispatch count that
both policies happen to satisfy for its input shape; a one-line assertion that the opener
produced no event would make it discriminate. That is recorded as a nit, not a deletion.
---
## Independent walk of the validator's evidence
Verdict `pass`, table `[3/4 validated · 1 missing dep]`. I opened every cited log.
| Row | Cited log | What the log actually shows |
|-----|-----------|------------------------------|
| `00-dynamo-editable-install` | `…20-58-28.320Z-bash-67ab.log` | `pytest --version` 9.0.3, pydantic 2.12.5, maturin 1.14.1, uv 0.12.0, `import dynamo, dynamo._core` succeeding. Real execution. |
| `01-python-lint` | `…21-02-01.063Z-bash-25f2.log` | `pre-commit run --files …` over the five changed files, `rc=0`, clean `git status` after. Python hooks report "no files to check" — correct, the diff touches zero `.py` files, and the log proves that with `git diff --name-only \| grep -c '\.py$'` → 0. Not a skipped run masquerading as a pass. |
| `02-rust-cargo-check` | `…21-10-44.421Z-bash-bdb1.log` | `fmt rc=0`, `clippy rc=0`, `test result: ok. 2451 passed; 0 failed; 5 ignored` — at the restored HEAD, with the sha256 printed. Supporting logs show `cargo check --workspace --all-targets` compiling `dynamo-llm` (`…20-59-07.417Z-bash-871d.log`) and clippy compiling it on both toolchains (`…21-01-49.817Z-bash-2cc5.log` 0.1.93, `…21-06-40.493Z-bash-47c9.log` 0.1.96). |
| `07-agg-smoke` | `…21-12-57.252Z-bash-d838.log` | Genuinely blocked, honestly labelled: vLLM engine-core init fails with "driver … too old (found version 12080)" against a `cu130` build; the worker exits at attempt 8 and `/health` reports zero instances. This is a host driver/runtime mismatch, not a fault of the change, and the validator recorded it as `missing dep` rather than grading over it. |
Per-section logs corroborate the specific claims: the three named aggregator regressions pass
by name (`…21-06-09.973Z-bash-d693.log`), all five `tool_call_merge` tests pass by name
(`…21-06-19.151Z-bash-f8d5.log`), all sixteen `_13972` tests pass by name and
`test_json_scanner_boundaries` plus the twelve pre-existing `test_tool_dispatch_*` tests pass
by name (`…21-05-55.508Z-bash-ab09.log`). The validator also disclosed, rather than buried,
an earlier aborted attempt visible in that same log where an invalid libtest flag produced
`rc=101` three times; the `d693` log supersedes it and the disclosure is accurate.
New test infrastructure — `tool_call_chunk`, `make_choice_with_tool_calls`,
`drive_to_tool_calls_finish`, `feed_fragments`, `assembled_arguments`, `scan_all`, and the
new inner-index parameter on `make_choice_with_tool_call` — is exercised, not merely
registered: every helper is on the call path of tests that appear by name in the `ab09` and
`481f` logs.
**On the missing row, and the fact that `openai.rs` is no longer byte-identical to `main`.**
The brief asks me to say plainly whether this is disqualifying. It is not, and here is the
reasoning rather than an assertion. The validation is unqualified on its verdict word and on
substance: every recipe capable of exercising the changed code ran and passed, the code
compiled and its tests executed at the reviewed SHA, and the one missing recipe is blocked by
a host driver/CUDA mismatch that predates the change and is independent of it. What that row
would have bought is a general "the frontend still serves" signal on an aggregated
deployment; it would not have exercised this feature, which is off unless
`--enable-streaming-tool-dispatch` is set and a tool-calling model is driven. So the honest
statement of the gap is not "the smoke would have proven this" but rather: **the edited SSE
handler has no runtime proof in this sandbox at all, and the assurance behind this change is
unit-level.** That assurance is unusually strong for unit-level — the tests call the real
`streaming_tool_dispatch_events` and assert on the real serialized SSE payloads, the pure
functions carry all of the new logic, and the handler diff is two lines that change a type
and pass it — but it is still unit-level, and the human reviewer should know that rather than
infer it. It is a note, not a finding, because I can point to no defect it conceals.
---
## Non-goals: none crossed
`git diff --name-only b4338ab87..HEAD` lists exactly five files. There is no change to
`DeltaAggregator`'s merge semantics (its call site discards the new outcome, deliberately and
with a comment); no parser-v2 or converter edit; no Python file at all, so no postprocessor
cadence work; and item 3 of my previous review remains report-only — the merge function's
mutation arms are untouched, so a conflict changes what the *dispatcher* does and nothing
about what the aggregator produces. The ordinary `data:` stream has no diff hunk anywhere in
it. The extension stays opt-in: `grep` over the diff finds
`DYN_ENABLE_STREAMING_TOOL_DISPATCH` only in doc comments, and `frontend_config.rs`,
`service_v2.rs`, and `frontend_args.py` are not in the diff, so the default remains false.
---
### Findings
| Location | Severity | Claim | Evidence |
|----------|----------|-------|----------|
| `lib/llm/src/http/service/openai.rs:2788` | nit | `is_exact_replay` compares only `function.arguments` against the *whole* accumulated string, so an exact replay is recognised only for calls that arrived in one chunk. A producer that repeats the final fragment of a multi-fragment call after emission takes the "continuation after the call was already dispatched" branch and logs a `warn!` accusing it of a protocol violation. | `:2789-2795` reads `entry.accumulated.function.arguments` and compares it to the incoming chunk's fragment; for a call assembled from `{"a":` + `1}` the accumulated value is `{"a":1}` and a replayed `1}` cannot match. Log-level only — no event is emitted on either path (`:2853-2862`), so behaviour is unaffected. |
| `lib/llm/src/http/service/openai.rs:2814` | nit | `assembly_has_identity` tests `is_some()`, not non-emptiness, so a producer that opens with `id: ""` / `name: ""` and supplies the real values in a later delta will dispatch a call carrying the empty id and name — first-wins keeps the empty opener. A harness cannot correlate a tool result to `id: ""`. | `:2815-2820`. Inherited from `main` (the old predicate also accepted `Some("")` for `id`) and consistent with the aggregator's first-wins, so not a regression introduced here; the merge test `empty_established_identity_value_is_not_a_conflict` (`tool_call_merge.rs:198-210`) pins the merge half of it deliberately. Tightening the dispatcher-side check to non-empty would be a one-line hardening. |
| `lib/llm/src/http/service/openai.rs:8661` | nit | `test_13972_nested_and_array_roots_complete` asserts only the final dispatch count, an assertion the pre-change same-chunk policy also satisfies for its input shape — it is one of the three tests that survived the in-place revert experiment. It still binds the new scanner, so it is not tautological, but it does not discriminate against the old policy. | The revert log records it as one of `3 passed`. Adding an assertion that the opener fragment produced no event, as the sibling `test_13972_identity_opener_then_argument_fragments` does, would make it discriminate. |
| `lib/llm/src/http/service/openai.rs:8898` | nit | `test_13972_dispatch_event_precedes_the_completing_fragment` discharges the issue's stream-level requirement (item 12) by *simulating* the handler loop in the test body — it collects side-channel events, then appends a placeholder `data:{i}` — rather than driving the real `async_stream::stream!` body. It therefore pins the ordering contract of `streaming_tool_dispatch_events`, not of the handler that calls it. | The test builds its `wire` vec by hand at `:8925-8936`. The production ordering is correct (`:3352-3369` pushes dispatch events into `events` before `EventConverter` runs) and the handler diff is two lines, so residual risk is small — but this is the one place where the issue asked for a stream-level proof and got a state-machine proof. |
| `change-validation.md` (artifact, not code) | nit | The validation record says the branch is "three commits ahead of merge-base `b4338ab87`"; `git log b4338ab87..HEAD` shows four. `change.md` has it right. | Bookkeeping only; the SHA, the diff, and every recipe row are correct. Internal artifact — nothing to fix in the change, and no entry in `review-findings.json`. |
No blocking findings.
---
### What the human reviewer and the PR description should still be told
1. **This re-times an opt-in feature for its existing consumers.** Before this change, a
backend that put `id`, `name`, and `arguments` on one chunk got a `tool_call_dispatch`
event on that chunk. After it, a call whose arguments are `Some("")` or absent — the
parameterless case — no longer dispatches on arrival; it dispatches at
`finish_reason: "tool_calls"`. That is exactly what the issue asks for and it is the only
way to disambiguate an empty opener from a parameterless call, but a harness that today
starts a parameterless tool the moment the opener arrives will observe it later than it
used to. `change.md` names this in its residual-risk section; the PR description should
too.
2. **A previously-dispatched shape can now become a permanent non-dispatch.** `}{"x":1}`,
leading junk, and a truncated prefix used to emit (wrongly); they now never emit. That is
the fix, but for anyone whose harness depended on the malformed event arriving it is a
visible behaviour change. The ordinary tool-call deltas still carry the call, so nothing
is lost from the standard stream.
3. **The assurance is unit-level.** The handler integration and the SSE wire ordering are
proven by in-process tests over the real dispatch function and real serialized events, not
by an end-to-end streaming run against a live engine. An integration test that drives the
handler with `--enable-streaming-tool-dispatch` and a fragmenting backend would close the
one gap the unit tests cannot reach (finding 4 above).
4. **This lands ahead of #13821.** The issue notes that the failure becomes operationally
important once the Python vLLM postprocessor restores immediate fragment publication. This
change is the prerequisite, and it is correct standalone, but the pair should be validated
together when #13821 lands. |
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Factory implementation notes. These explain non-obvious constraints in the change; they are not review findings.
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No actionable comments were generated in the recent review. ℹ️ Recent review info
WalkthroughThe OpenAI streaming path now assembles fragmented tool-call arguments by choice and tool-call index. It validates JSON completion, handles terminal calls, detects conflicts, prevents duplicate dispatch, and documents the behavior. ChangesTool-call dispatch
Priority: Estimated code review effort: 4 (Complex) | ~45 minutes Severity of issue fixed: Medium Merge Risk:
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| Check name | Status | Explanation |
|---|---|---|
| Linked Issues check |  |
The PR meets the coding requirements in issue #13972. The Rust streaming path keeps request-local state keyed by choice and tool-call index. Shared merge logic concatenates argument fragments and appl… |
| Out of Scope Changes check | |
The changed files stay within issue #13972. The shared merge module and aggregator update support consistent tool-call reconstruction. The HTTP integration tests verify the required streaming behavior… |
| Title check | |
The title clearly identifies the primary fix: preventing tool_call_dispatch from sending truncated arguments to harnesses. The frontend scope is slightly broad, but the title remains directly related … |
| Description check | |
The description is comprehensive and covers the change overview, implementation details, limits, validation results, and linked issue. It does not use the template headings exactly and omits the Pull … |
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Explanation
The PR meets the coding requirements in issue
#13972. The Rust streaming path keeps request-local state keyed by choice and tool-call index. Shared merge logic concatenates argument fragments and applies first-non-empty identity handling with conflict reporting. The dispatch state machine validates JSON incrementally, suppresses malformed, incomplete, duplicate, conflicting, and invalid continuation calls, and handles terminal parameterless calls. The implementation preserves ordinary SSE data, emits the opt-in event before the completing ordinary chunk, applies parallel-call filtering, preserves the existing event payload, and remains disabled by default. Focused merge, state-machine, malformed-input, deduplication, scanner, and HTTP SSE regression tests cover the required behavior. Documentation describes assembly, syntax validation, and client schema and execution responsibility.
Full details: Out of Scope Changes check
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The changed files stay within issue
#13972. The shared merge module and aggregator update support consistent tool-call reconstruction. The HTTP integration tests verify the required streaming behavior. The documentation update covers the required dispatch guarantees. No unrelated Python vLLM cadence change or unrelated protocol-path change is present in the supplied change summary.
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The title clearly identifies the primary fix: preventing tool_call_dispatch from sending truncated arguments to harnesses. The frontend scope is slightly broad, but the title remains directly related to the main change.
Full details: Description check
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The description is comprehensive and covers the change overview, implementation details, limits, validation results, and linked issue. It does not use the template headings exactly and omits the Pull Request Checklist section, but the required information is present overall.
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Inline comments:
In `@lib/llm/src/http/service/openai.rs`:
- Around line 2953-2958: Update the terminal finish-reason gate in the
accumulation logic so both FinishReason::ToolCalls and FinishReason::Stop
proceed to the existing usable validation and dispatch path. Keep other finish
reasons marking unfinished entries as AssemblyState::Invalid, and leave the
downstream usable check unchanged so incomplete arguments remain rejected.
In `@lib/llm/src/protocols/openai/chat_completions/tool_call_merge.rs`:
- Around line 79-87: Update the identity merge logic for the relevant fields in
the tool-call merge path so a non-empty incoming value replaces an established
empty accumulator value, while an empty incoming value remains a no-op and
differing non-empty values still report a conflict. Apply the same behavior to
both ID and name handling, and update
empty_established_identity_value_is_not_a_conflict to assert the real ID and
name are retained with the Merged outcome.
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docs/fern/pages/blog/2026/agentic-harness-support.mdxlib/llm/src/http/service/openai.rslib/llm/src/protocols/openai/chat_completions.rslib/llm/src/protocols/openai/chat_completions/aggregator.rslib/llm/src/protocols/openai/chat_completions/tool_call_merge.rs
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CI result: passed All checks on Longest-running jobs: Skipped by path filters: Note that this is the pre-merge check set. Full CI on this repository runs only after a maintainer comments |
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Validation status: incomplete Head is now Round 2 (
Both new tests were checked against deliberate reversions of the code they guard, so they are known to be discriminating rather than tautological: reverting the early confirmation to Why this is incomplete, and what needs a maintainer The automated updater that owns the visible title and description declined to edit them, for the same reason as after the previous round: this request carries no record that the factory owns that copy, and that record can only be created when the request is opened. Rather than overwrite text I cannot prove is mine — it may contain a maintainer's edits — the title and description are untouched. This is not a transient failure, so it will recur on any further round. That leaves the description describing an earlier head. Seven of its claims are now wrong:
Corrected text is prepared and can be applied once ownership is recorded, or a maintainer can edit the description directly. The review threads are left open for the same reason: replying and resolving are gated behind that same ownership check. The code addressing them is pushed and green, so please read the threads against |
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Two P2 findings from the exact-head local review.
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@coderabbitai full review @devin-ai-integration review this PR at current head 3d438cb. |
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✅ Action performedFull review finished. |
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nursery: @dynamo-ops please run full CI for 98d8d6b |
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/ok to test 98d8d6b |
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nursery: @dynamo-ops please run full CI for 5486b0b |
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/ok to test 5486b0b |
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nursery: @dynamo-ops please run full CI for a31e59b |
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/ok to test a31e59b |
This was referenced Oct 31, 2026
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main stopped compiling lib/llm/tests/streaming_tool_dispatch_http.rs when ai-dynamo#13986 merged: its chunk() helper builds NvCreateChatCompletionStreamResponse field by field and predates the model_eos field from ai-dynamo#17625. This is the same one-line change as ai-dynamo#18553, so the two merge cleanly in either order. Signed-off-by: Bindu Bhargava R Chintam <bindubhargavareddy@gmail.com>
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Summary
The opt-in
tool_call_dispatchSSE extension previously treated an argument fragment as a complete call when one delta also carried its ID and name. Later argument fragments could then be suppressed, leaving the harness with truncated arguments.The dispatcher now assembles calls per request, choice index, and tool-call index. It uses
merge_tool_call_chunk, also used by the non-streaming aggregator, to keep the first non-empty ID and name and concatenate argument fragments. The aggregator continues to apply its existing terminalLengthfiltering.Objects and arrays can dispatch early after the incremental scanner finds a closing boundary,
serde::de::IgnoredAnyconfirms valid JSON syntax, and the ID and name are known. Scalar arguments wait forToolCallsorStop; absent or empty arguments also wait for one of those terminal reasons and are then accepted for parameterless calls. The argument string is forwarded unchanged. This checks JSON syntax, not the tool schema or permission to execute it.Malformed arguments and conflicting identities detected before dispatch suppress that call. An emitted event cannot be retracted: later chunks for its choice and call index are suppressed, and a differing continuation produces a warning. Terminal calls are considered in call-index order.
Limits
Dispatch remains disabled by default and requires
--enable-streaming-tool-dispatchorDYN_ENABLE_STREAMING_TOOL_DISPATCH. Assembly only observes the deltas after the handler's existing single-tool filtering. It does not replace or rewrite ordinary SSE data frames. The handler yields a dispatch event before the ordinary frame that completes that call.The HTTP tests use
HttpServicewith a scripted backend and inspect actual SSE frames for event order, preservation of argument fragments, and suppression of truncated arguments. They do not run a live inference engine.Reviewer Start
update_tool_call_assembly,finalize_choice_assemblies, andis_exact_replayinlib/llm/src/http/service/openai.rsfor dispatch completion, terminal handling, and duplicate detection.lib/llm/src/protocols/openai/chat_completions/tool_call_merge.rsfor the shared identity and argument merge policy.lib/llm/tests/streaming_tool_dispatch_http.rsfor the real HTTP tests of event order, ordinary frames, and truncated arguments.Validation
a31e59b3399d1dc4e15a6c65375507c5d486d565. Pre Merge and full CI completed successfully on October 29, 2026. All seven required checks passed:copyright-checks,DCO,codeowners,pre-merge-status-check,backend-status-check,deploy-status-check, anddynamo-status-check. Workspace and Python-binding Rust tests and all Rust Clippy jobs passed. Skipped jobs are not counted as successful tests.5486b0ba9found that the HTTP fixture lacked upstream's newmessage_boundaryfield. Commita31e59b3399d1dc4e15a6c65375507c5d486d565initializes it toNone, matching upstream fixtures. Clippy on the merged base passed. Rustfmt passed before this commit; no local tests, builds, or benchmarks ran. The earlier head's failing and superseded CI results do not validate this repair.5486b0ba98ce0e23e59728cbcd7907a819ad166f. On October 29, 2026, mergedmainatf3fd065ca3389d0bbb7471502fbe674f2be6000fin56a1cc933dfd3e1b55db0f1552e9690b2ca600a4to resolve confirmed conflicts. The shared merge helper now preserves upstream custom-tool input assembly, and the aggregator keeps its terminalLengthfiltering.5486b0ba98ce0e23e59728cbcd7907a819ad166flimits scanner whitespace to the four JSON whitespace bytes.test_13972_invalid_whitespace_before_identity_never_dispatchescovers a form-feed fragment arriving after a closed root but before identity. The HTTP fixture now bounds its requests, and the blog describes both terminal reasons and the limits of conflict suppression.98d8d6b8dfb1d674090066584acb5436a49bc315. Mergedmainat17bffaf9c708de80c5d197cd2539022b7f6a51f0to resolve the confirmed conflict inmake_choice_with_tool_call. The merge keeps the PR's explicit call-index helper and addscustom: Noneto its new tool-call values for the updated protocol type.tool_call_completionfield. Commit98d8d6b8dfb1d674090066584acb5436a49bc315initializes it to an empty vector, matching existing fixtures. Rustfmt passed for the edited file.dispatch_event_precedes_the_completing_frame_on_the_wire,truncated_arguments_never_dispatch_on_the_wire, andtest_13972_out_of_range_exponent_dispatchespassed on this head. Thepre-merge-status-check,dynamo-status-check,backend-status-check, anddeploy-status-checkgates passed. Skipped jobs are not counted as successful tests. Full CI was requested once for this head.aa234ca59bf698f0fa5600ead19dd2f439585d5e, passed Pre Merge and full CI on October 7, 2026. Its remote workspace test log confirmed both HTTP streaming-dispatch tests and the out-of-range JSON-number regression passed. Skipped jobs are not counted as successful tests.Related Issues
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Improvements
Documentation
Tests