fix: prevent clip watch from skipping images

[Luqueee]

Summary

Fixes #12.

Client.Watch now advances its watermark from the Last-Modified value returned by the exact GET that was processed. It no longer performs a follow-up HEAD that can observe a later publication and skip it.

Validation

• go test ./...
• go test -race ./...
• go vet ./...
• git diff --check

Added a deterministic regression test that publishes a second image while the first GET is still in progress and verifies both images are observed.

[coderabbitai]

No actionable comments were generated in the recent review. 🎉

ℹ️ Recent review info

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📥 Commits

Reviewing files that changed from the base of the PR and between 03db9ab and e42d6f1.

📒 Files selected for processing (2)

• internal/clip/client.go
• internal/clip/client_test.go

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📝 Summary

Summary by CodeRabbit

• Bug Fixes

  • Improved image watching to reliably detect newly published images without skipping updates during concurrent publishing.
  • Uses timestamps from image retrieval responses to maintain accurate update tracking.

• Tests

  • Added coverage for concurrent image publishing to verify that all available images are delivered.

Walkthrough

Changes

Watch watermark race fix

Layer / File(s)	Summary
Return the GET timestamp internal/clip/client.go	The internal pull operation now returns the downloaded path and parsed GET Last-Modified timestamp. Error paths return a zero timestamp.
Update Watch watermark from the pull internal/clip/client.go, internal/clip/client_test.go	Watch uses the GET timestamp, with a HEAD fallback when needed. A synchronized regression test verifies that images published during a pull are both delivered.

Merge Risk: ⚪ Minimal · up to e42d6

Watch now retains the processed image timestamp, preventing a concurrently published image from being skipped; the regression test covers this sequence. No current merge-blocking risk remains.

🚥 Pre-merge checks | ✅ 4

✅ Passed checks (4 passed)

Check name	Status	Explanation
Title check	✅ Passed	The title uses the required Conventional Commit format and clearly describes the fix to prevent image skips in clip Watch.
Description check	✅ Passed	The description explains the watermark fix, the regression scenario, the added test, and the validation commands. It is directly related to the changeset.
Linked Issues check	✅ Passed	The changes satisfy issue #12. Watch uses the Last-Modified value from the processed GET, retains fallback behavior for missing or invalid headers, and adds a deterministic regression test.
Out of Scope Changes check	✅ Passed	The changes are limited to the Watch watermark fix and its regression test. No unrelated code changes are identified.

✨ Finishing Touches

📝 Generate docstrings

• Create stacked PR
• Commit on current branch

🧪 Generate unit tests (beta)

• Create PR with unit tests
• Commit unit tests in branch codex/fix-clip-watch-watermark

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