fix(gh-comment-attach-files): retry uploads and fix URL detection

[shunk031]

Summary

• Add up to 3 retries for file uploads
• Fix false-positive bug in URL detection logic
• Refactor perform_upload() to return results instead of raising immediately
• Improve robustness of run_playwright_value()
• Default to headless browser; add --headed opt-in flag
• Detect GitHub login redirects and surface a clear error message

Changes

1. Retry logic (upload_files)

Handles upload failures in unstable environments (CI, slow networks, etc.).
Retries up to 3 times with appropriate recovery per failure type:

Failure	Recovery
CalledProcessError (crash)	Wait 30s → reopen browser
upload_result.ok == false	Wait 60s → reload page
URL not found	Wait 30s → retry

2. URL detection false-positive fix

Problem: GitHub inserts a temporary placeholder ![Uploading stagedName…]() into the textarea immediately after receiving a file. The old implementation matched on stagedName and incorrectly treated this as a completed upload.

Fix: Drop the stagedName check; instead compare the count of URL hint occurrences before and after the upload:

// Before
return value.includes(stagedName) || urlHints.some(h => value.includes(h));

// After
const countHints = (text) => urlHints.reduce((sum, h) => sum + (text.split(h).length - 1), 0);
return countHints(value) > countHints(previous);

3. Headless-by-default with --headed opt-in

Previously the browser always launched in headed (visible) mode, which interrupted other work with unexpected windows.

• Default: headless — no browser window appears during normal use.
• --headed: opt-in flag for when a GitHub login is needed.
• Login detection: if wait_for_comment_composer detects a /login or /session redirect, it exits immediately with a clear message pointing the user to --headed.

4. Other

• perform_upload(): return result instead of raising; retry control consolidated in caller
• run_playwright_value(): handle "undefined" stdout and JSONDecodeError
• wait_for_comment_composer(): unify error message to a single line
• import sys moved to top-level; remove __import__("sys") workaround

🤖 Generated with Claude Code

[codecov]

Codecov Report

✅ All modified and coverable lines are covered by tests.
✅ Project coverage is 88.79%. Comparing base (520d850) to head (810ed77).
⚠️ Report is 1 commits behind head on main.

Additional details and impacted files

@@            Coverage Diff             @@
##             main     #457      +/-   ##
==========================================
- Coverage   88.93%   88.79%   -0.15%     
==========================================
  Files           9        9              
  Lines         235      232       -3     
==========================================
- Hits          209      206       -3     
  Misses         26       26              

Flag	Coverage Δ
macos-14-client	41.66% <ø> (ø)
ubuntu-latest-client	88.36% <ø> (+1.66%)	⬆️
ubuntu-latest-server	88.74% <ø> (-0.10%)	⬇️

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