bug(embedder): extractLeadingComment crashes on out-of-bounds line access

[carlos-alm]

Found during dogfooding v2.4.0

Severity: Medium
Command: codegraph embed -m minilm --strategy structured

Reproduction

1. Build a graph: codegraph build .
2. Switch to a branch where some files were renamed/deleted (stale node data)
3. Run: codegraph embed -m minilm --strategy structured

Expected behavior

Should gracefully skip symbols with invalid line numbers.

Actual behavior

TypeError: Cannot read properties of undefined (reading 'trim')
    at extractLeadingComment (embedder.js:138:30)
    at buildStructuredText (embedder.js:200:19)

Root cause

extractLeadingComment(lines, fnLineIndex) doesn't bounds-check lines[i]. When fnLineIndex > lines.length (stale graph data), lines[i] is undefined.

Suggested fix

Add bounds check at the top of the loop in extractLeadingComment:

if (i >= lines.length) continue;

Or clamp fnLineIndex to lines.length before starting the loop.