codex-copilot-instruction-mirrors-document-defective-csharp-toolchain-commands

• Date captured: 2026-08-11
• Author: Dan Moisan
• Status: Pending promotion to GitHub issue

Automation note: Keep the section headings below unchanged; the promotion tooling maps each of them into the GitHub bug issue template.

• Last Updated: 2026-08-11

Summary

Feature 2026-08-10-csharp-toolchain-gate-fidelity-512 (issues #492, #509, #512, #522) corrected the
C# format, analyzer and type-check commands in CLAUDE.md, .claude/rules/csharp.md and
.claude/skills/csharp-qa-gate/SKILL.md. It deliberately excluded the Codex/Copilot instruction
mirror tree under scope decision SD1. Those mirrors still document the CSharpier v0 bare-path form
(csharpier .) and the unpassable /t:Build ... /p:Nullable=enable nullable command. After that
feature merges, the mirrors become the only sites in the repository that disagree with
.github/workflows/ci.yml, so the divergence becomes host-dependent (Claude sessions read the
corrected files; Codex/Copilot sessions read the stale mirrors) and correspondingly harder to
diagnose.

Environment

• OS/version: Windows 11 Pro 10.0.26200
• Runtime: .NET Framework 4.8.1; MSBuild from Visual Studio 18 (Community); repo-pinned .NET SDK 8.0.205; CSharpier pinned to 1.2.6 in dotnet-tools.json
• Command/flags used: git grep -n -E 'csharpier[[:space:]]+\.' and git grep -n -F 'Nullable=enable' over tracked files
• Data source or fixture: the repository's own governance and instruction files

Steps to Reproduce

1. From the repository root, run
   git grep -n -E 'csharpier[[:space:]]+\.' -- ':!docs/features' ':!docs/research' ':!.claude/agent-memory'
2. Run
   git grep -n -E '(/t:Build.*Nullable=enable|Nullable=enable.*/t:Build)' -- ':!docs/features' ':!docs/research' ':!.claude/agent-memory'
3. Observe that after feature 512 merges, every remaining hit is inside the mirror tree enumerated
   below.

Expected Behavior

Every site in the repository that documents a mandatory toolchain command documents a command that
executes against the pinned toolchain, enforces the policy it names, and agrees with
.github/workflows/ci.yml, regardless of which agent host reads it.

Actual Behavior

Eight mirror files still document at least one defective command. Verified by grep on 2026-08-10 and
re-verified on 2026-08-11 after feature 512's corrections
(docs/features/active/2026-08-10-csharp-toolchain-gate-fidelity-512/evidence/qa-gates/site-inventory-reconciled.2026-08-11T00-18.md):

Path	Lines	Defect
AGENTS.md	466 (false rationale), 469, 470 (format), 487, 488 (type-check), 660 (format), 662 (type-check)	all
.github/instructions/csharp-code-change.instructions.md	29 (false rationale), 32, 33 (format), 50, 51 (type-check)	all
.github/instructions/csharp-unit-test.instructions.md	45 (format), 47 (type-check)	format + type-check
.agents/skills/csharp/SKILL.md	17 (format), 19 (type-check)	format + type-check
.agents/skills/csharp-qa-gate/SKILL.md	32 (format), 34 (type-check)	format + type-check
.github/agents/csharp-typed-engineer.agent.md	172 (format), 174 (type-check)	format + type-check
.github/agents/csharp-atomic-executor.agent.md	258 (format), 260 (dotnet build -p:Nullable=enable)	format + type-check
.codex/codex-web-setup.sh	342 (printed follow-up command inside the heredoc ending at line 348)	type-check

Note on .codex/codex-web-setup.sh:342: it is a documentation carrier, not an executable one —
lines 336-347 sit inside a heredoc terminated at line 348 and are printed as "useful follow-up
commands", not executed. Feature 512 handled its practical consequence by retaining
-EnableNullable on scripts/vscode/Invoke-VSBuild.ps1 as a warning-emitting no-op, so the printed
command still binds.

Logs / Screenshots

• Attached minimal logs or screenshot
• Snippet: after feature 512's corrections, git grep -n -E 'csharpier[[:space:]]+\.' over tracked
  files (excluding docs/features, docs/research and .claude/agent-memory) returns 10 hits,
  all inside the mirror tree; the same-line /t:Build + Nullable=enable grep returns 9 hits,
  all inside the mirror tree.

Impact / Severity

• Blocker
• High
• Medium
• Low

A Codex- or Copilot-driven session reading a mirror will still run the unpassable nullable command
and can still manufacture the false blocking CS86xx findings that required human-level override on
deliveries #507 and #508 on 2026-08-08. It will also run a format command that returns exit 1 and
formats nothing.

Suspected Cause / Notes

Recorded as scope decision SD1 of
docs/features/active/2026-08-10-csharp-toolchain-gate-fidelity-512/spec.md. The exclusion rests on
four grounds, in descending strength:

1. .github/instructions/ sits under an unsuspended hard constraint.
   .claude/skills/policy-compliance-order/SKILL.md states: "Do NOT modify policy documents under
   .claude/rules/ or .github/instructions/." The epic
   build-ci-coverage-gate-fidelity's "Execution Authorization Required" section suspended that
   constraint for feature 512 only for CLAUDE.md and .claude/rules/csharp.md.
   .github/instructions/ therefore requires its own authorization grant, equivalent to the one
   the epic issued for .claude/rules/csharp.md.
2. AGENTS.md forbids manual editing and its generator does not exist here. AGENTS.md lines
   3-27 declare the file generated from seventeen .github/** sources, say "Do not edit this file
   manually", and name scripts/dev-tools/sync-agents-from-instructions.ps1 as the regeneration
   command. scripts/dev-tools/ contains exactly one file, run-actionlint.ps1; the named
   generator does not exist in this repository. Hand-editing violates the file's own contract;
   regenerating is impossible here.
3. .agents/, .codex/ and .github/agents/ are inbound artifacts of a different repository.
   They self-describe as Codex push-down resources installed by the drm-copilot MCP tool
   push_down_codex_and_agents_customizations. drm-copilot is the owning repository for
   .agents/, .codex/ and .github/agents/. An edit here is not durable; the next push-down
   overwrites it.
4. .github/agents/** is excluded on ground 3 only. If a reviewer disputes drm-copilot ownership
   of .github/agents/, this issue is the correct place to resolve it.

Additional residuals folded into this entry

• .csharpierignore comment residual. .csharpierignore lines 1-3 and 9-11 repeat the same
  false premise feature 512 removed from CLAUDE.md ("CSharpier formats C# source only (per
  CLAUDE.md C#1)"). The ignore rules are correct; only the explanatory comment is wrong. The file
  is outside feature 512's enumerated documentation sites.
• TaskMaster/Ribbon/EngineCommandCatalog.cs:93 comment residual. The comment reads
  // returns false. This keeps the file clean under /p:Nullable=enable. It cites
  /p:Nullable=enable as the enforcing gate, which is false after feature 512 — the gate now
  relies on the per-file #nullable enable pragma plus /p:TreatWarningsAsErrors=true. It could not
  be corrected in feature 512 because that feature makes no *.cs change.
• .claude/rules/powershell.md:18 residual. That line states the Pester step should "use repo
  config at scripts/powershell/PoshQC/settings/pester.runsettings.psd1". That path does not exist
  in this checkout: ls scripts/ returns only dev-tools/, temp-extract-coverage.ps1 and
  vscode/; find . -name "pester.runsettings*" and find . -type d -name "PoshQC" both return no
  matches. PoshQC is entirely MCP-server-side here. This is the same class of defect as feature 512's
  — a documented command referencing something that does not exist — in a different rule file, and
  .claude/rules/powershell.md was not covered by the epic's authorization. Recorded in
  docs/features/active/2026-08-10-csharp-toolchain-gate-fidelity-512/evidence/baseline/baseline-powershell-toolchain.2026-08-10T15-40.md.

PowerShell coverage shortfall: none to fold in. Feature 512's [P0-T16] measured line coverage of
scripts/vscode/Invoke-VSBuild.ps1 at 85.71%, at or above the 85% policy floor, so no
PREEXISTING_COVERAGE_SHORTFALL: was recorded and [P6-T4] had nothing to fold into this entry.

Proposed Fix / Validation Ideas

• Unit coverage areas: not applicable — documentation corrections. If a toolchain-command lint is
  added, assert that every documented command in every instruction mirror is executable against
  the pinned tool versions and agrees with .github/workflows/ci.yml.
• Integration scenario to retest: after correction, re-run the three greps from feature 512's
  [P5-T11] and confirm zero hits outside the permitted residual classes.
• Manual verification notes: (a) obtain an explicit authorization grant for
  .github/instructions/ equivalent to the epic's grant for .claude/rules/csharp.md;
  (b) correct .github/instructions/*.instructions.md under that grant; (c) either restore the
  AGENTS.md generator or agree a policy for maintaining the generated file; (d) raise the
  .agents/, .codex/ and .github/agents/ corrections upstream in drm-copilot so the next
  push-down carries them; (e) correct the .csharpierignore comment, the
  EngineCommandCatalog.cs:93 comment, and .claude/rules/powershell.md:18.

Next Step

• Promote to GitHub issue (bug-report template)
• Move to active fix folder / branch