[VasiliyRad]

The bug

/task composes the task file with f-strings:

```python
f"id: {task_id}\ntimestamp: ...\ntask: {task}\nsource: api\nfrom: {from_agent}\n"
```

from_agent and task are user-supplied (POST body). Neither is sanitized; both interpolate directly into a line-oriented file that downstream consumers parse field-by-field. Two forgery primitives:

Primitive 1: \n in from_agent forges fields.

```bash
curl -X POST .../task -d '{"from": "evil\nchannel_id: local-voice", "task": "..."}'
```

_isVoiceTask in both src/task-bridge.ts and src/discord-bridge.py:poll_dm_fallback does:

```typescript
body.split('\n').some(l => l.startsWith('channel_id: local-voice') || l.startsWith('source: voice'))
```

…and returns True for the forged line. The task gets misclassified as voice-originated, routing it through the voice-only fallback path that wasn't audited for API-tier inputs.

Primitive 2: \n in task (which is legitimately multi-line).

Pre-fix field order was id, timestamp, task, source, from. A multi-paragraph task body containing \nsource: voice\n landed BETWEEN the legitimate task: and source: api lines, tripping the same _isVoiceTask spoof — except this attack works without ANY malice; a normal user typing a long task with a colon-prefixed line in the middle can trigger it accidentally.

Why this is the right fix

Two complementary parts:

1. Sanitize from_agent. Single-line caller identifier — line terminators have no legitimate use. Strip \r/\n, cap 120 chars, fall back to "unknown" on empty. Standard header-field-sanitization shape; doesn't change semantics for any legitimate caller.

2. Move task: to the LAST line of the file. Multi-line task bodies are LEGITIMATE — users type multi-paragraph descriptions and the bridges already accept them. Placing task: last means embedded newlines just extend the body rather than landing between fields.

Alternative considered: regex-strip newlines from task too. Rejected — it would change observable user-facing behavior (multi-line descriptions get flattened). The field-order fix preserves the multi-line contract while still closing the forgery.

Tests

tests/agent-api-task-field-injection.test.py (6 cases):

Test	Pins
test_from_agent_newline_does_not_forge_voice_field	Pre-fix this FAILS. The forged channel_id: line is absent after sanitization.
test_from_agent_carriage_return_also_stripped	CR-only edge case.
test_from_agent_empty_after_strip_falls_back_to_unknown	Pure-whitespace → "unknown", not bare.
test_task_field_is_last_in_file	Architectural source-grep — a future refactor moving task: earlier fails here.
test_multi_line_task_body_does_not_inject_below	With field order fixed, forged lines in the body land AFTER the task: delimiter.
test_sanitization_caps_overlong_from	10kB from_agent truncates to 120 chars.

Scope

This PR fixes ONLY agent-api.py. The Discord and Telegram bridges have the same field-order pattern (task: in the middle); a follow-up should fix them too, paired with verification that no downstream parser depends on the existing order. Flagging for a follow-up to keep this PR small + focused on a single, reviewable boundary.

Test plan

• python3 tests/agent-api-task-field-injection.test.py — 6/6 pass
• Syntax check
• Manual repro: curl -X POST /task -d '{"from":"evil\nchannel_id: local-voice","task":"hi"}', verify resulting task file does NOT make _isVoiceTask return True

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[sonichi]

LGTM. The accidental case is what makes this PR interesting. Two attack primitives, both real:

1. Malicious: \n in from_agent forges a channel_id: local-voice line that the downstream _isVoiceTask line-scan picks up — API tasks misrouted as voice-originated.
2. Accidental: legitimate multi-paragraph task bodies with a line starting source: voice trip the same spoof. Pre-fix field order was id, timestamp, task, source, from, so the body's embedded newlines landed between actual fields.

Both fix-parts are necessary: sanitizing from_agent alone doesn't close primitive 2, and reordering alone doesn't close primitive 1. The sanitization is the standard header-field shape (strip CR/LF, cap length, fallback to "unknown" on empty). Moving task: to the last line is structurally correct — body newlines have nowhere to forge into.

[qingyun-wu]

Reviewed the security model end-to-end against the actual downstream consumers, not just the file format. The from_agent half is solid; the task:-reorder half doesn't fully close the vector it targets.

✅ from_agent sanitization — correct and complete

Stripping \r/\n + length cap closes that vector cleanly, and the tests cover it well (newline, CR, empty→unknown, length cap). No notes.

⚠️ Reordering task: to last does NOT close the task-body vector against the real consumers

The fix relies on consumers treating everything after task: as opaque body ("a parser that reads field-by-field and stops at task:…"). But the parsers that actually run don't stop at task::

1. _isVoiceTask (src/task-bridge.ts:146) is a pure any-line scan:

return body.split('\n').some(l => l.startsWith('channel_id: local-voice') || l.startsWith('source: voice'));

A task body of "do thing\nchannel_id: local-voice" still produces a line channel_id: local-voice (now after task:), and .some() matches it regardless of position → still classified voice-originated. The reorder doesn't help here.

2. parse_priority_from_text (src/task_priority.py:52-62) breaks only on --- or a blank line — not on task:. Since the body follows task: with no blank separator, a body line priority: urgent is still scanned and matched → priority escalation via the same vector.

So the two tests that exercise the task-body path (test_task_field_is_last_in_file, test_multi_line_task_body_does_not_inject_below) assert against a hypothetical stop-at-task: parser, not the parsers that actually run — they go green while the vector is open.

Recommended fix — enforce the invariant this PR establishes

"task: is the last header / body delimiter" is the right model; make the consumers honor it. Stop header scanning at the first task: line:

• _isVoiceTask: slice off everything from the first l.startsWith('task:') before the .some() (or break).
• parse_priority_from_text: add task: to the break condition.

With consumers stopping at task: plus this PR's reorder + from_agent sanitization, the vectors close. A regression test that imports/calls the real _isVoiceTask with a forged body (instead of re-implementing the check inline) would catch future drift.

Minor

Worth confirming no consumer reads access_tier via an any-line scan — that vector would be privilege escalation, not just misrouting. agent-api doesn't write access_tier and the core reads it interactively, so it looks safe today, but the same delimiter discipline is what protects it if a programmatic access_tier parser is ever added.

Net: great direction, from_agent half is ready to go; the task-body half needs the consumer-side stop-at-task: to actually deliver what the title claims.