feat(task): verify prompt file digests

[ALV0612]

Summary

• add optional --prompt-file-sha256 <digest> verification for task --prompt-file
• hash and decode one file buffer so approval, dispatch, and the receipt cannot refer to different reads
• preserve verified prompt-file text verbatim through turn/start, including leading/trailing whitespace and the common final newline
• expose the unambiguous promptFileSha256 receipt in foreground JSON and persisted background requests/results
• reject malformed/mismatched digests before creating a job or Codex thread

Codex review follow-up

Addressed the P2 finding in commit a8f21dd:

• removed the later prompt-file .trim() mismatch at the app-server transport boundary
• carried explicit prompt source metadata through detached workers
• renamed the raw-file receipt from promptSha256 to promptFileSha256
• added foreground and background regression tests with leading spaces, trailing spaces, and a final newline
• retained existing positional/stdin normalization and covered it separately

Verification

• OpenSpec change fix-issue-621-verify-prompt-file-digest: valid
• focused integrity/whitespace tests: 8/8 pass
• full test suite: 104/104 pass
• npm run build: pass
• npm run check-version: pass
• syntax checks and git diff --check: pass

Fixes #621

[chatgpt-codex-connector]

💡 Codex Review

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Reviewed commit: deebd7a815

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[ALV0612]

@codex review

[chatgpt-codex-connector]

Codex Review: Didn't find any major issues. What shall we delve into next?

Reviewed commit: a8f21dd608

ℹ️ About Codex in GitHub

Your team has set up Codex to review pull requests in this repo. Reviews are triggered when you

• Open a pull request for review
• Mark a draft as ready
• Comment "@codex review".

If Codex has suggestions, it will comment; otherwise it will react with 👍.

Codex can also answer questions or update the PR. Try commenting "@codex address that feedback".