🤖 fix: document vendor stamp-file handling

[ThomasK33]

Summary

This PR hardens vendor workflow guidance and removes fragile stamp-file behavior that caused CI drift.

Background

Agent runs were deleting vendor stamp artifacts unexpectedly. The prior Makefile relied on vendor/.modules.stamp, which is not stable under go mod vendor and led to verify-vendor check failures.

Implementation

• Updated Makefile to use vendor/modules.txt as the vendor freshness target marker:
  • VENDOR_STAMP := vendor/modules.txt
  • removed manual touch/directory creation for .modules.stamp
• Removed obsolete .modules.stamp ignore handling from .gitignore
• Updated AGENTS.md guidance to explicitly protect vendor/modules.txt and removed .modules.stamp references

Validation

• make verify-vendor
• make test
• make build
• make lint

Risks

Low. This aligns stamping with canonical go mod vendor output and reduces CI/local mismatch risk.

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[ThomasK33]

@codex review

Please review this PR.

[ThomasK33]

@codex review

Addressed CI feedback and updated the PR.

[chatgpt-codex-connector]

Codex Review: Didn't find any major issues. Nice work!

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[ThomasK33]

@codex review

Updated per reviewer direction:

• switched Makefile vendoring marker to vendor/modules.txt
• removed .modules.stamp handling
• aligned AGENTS guidance
  Please re-review.

[chatgpt-codex-connector]

Codex Review: Didn't find any major issues. Hooray!

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".

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[ThomasK33]

https://mux.md/s9tnG#8ncOrGDR0jAKLw