fix(indexer): UTF-8 encoding for git log on non-UTF-8 Windows locales

[rajkumarsakthivel]

Summary

Fixes #140. Git history indexing fails with UnicodeDecodeError on Windows machines using non-UTF-8 system locales (e.g. Korean cp949, Japanese Shift_JIS, Chinese GBK).

The two subprocess.run calls in index_commits used text=True without an explicit encoding=. Python decodes subprocess output using locale.getpreferredencoding(False), which on Windows returns the system ANSI codepage. Since git log output is always UTF-8, any non-ASCII commit message or author name that isn't valid in the system codepage raises UnicodeDecodeError.

Fix: pass encoding="utf-8", errors="replace" on both calls, matching git's actual output encoding. The errors="replace" fallback handles the rare case where git output contains non-UTF-8 bytes (e.g. legacy repos with Latin-1 commit messages) by substituting U+FFFD instead of crashing.

One-line change per call site, no new dependencies.

[Copilot]

Pull request overview

This PR fixes Windows git-history indexing failures caused by decoding git log output using the host locale (non‑UTF‑8 ANSI codepages like cp949/Shift_JIS), by explicitly decoding subprocess output as UTF‑8 with a non-fatal error strategy.

Changes:

• Add encoding="utf-8" to both subprocess.run(..., text=True) calls in index_commits.
• Add errors="replace" to prevent crashes on unexpected/non‑UTF‑8 bytes in git output.

Comments suppressed due to low confidence (1)

src/context_engine/indexer/git_indexer.py:47

• Same as above: if git is configured to output log text in a non-UTF-8 encoding, decoding as UTF-8 will replace characters and lose filenames/metadata context. Force git’s log output encoding to UTF-8 for this call as well to keep producer/decoder consistent.

        ["git", "log", range_arg, "--name-only", "--format=%H"],
        cwd=project_dir, capture_output=True, text=True,
        encoding="utf-8", errors="replace", check=False,

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[Copilot]

Pull request overview

Copilot reviewed 2 out of 2 changed files in this pull request and generated no new comments.

Comments suppressed due to low confidence (1)

tests/indexer/test_git_indexer.py:117

• The new non-ASCII test is likely to pass even on the pre-fix implementation because it doesn’t actually exercise the locale-driven decoding path that caused #140; it only asserts the decoded content. To make this a reliable regression test, spy on context_engine.indexer.git_indexer.subprocess.run and assert index_commits() passes encoding='utf-8' and errors='replace' (and avoid leaving nodes/edges unused, which Ruff will flag).

    chunks, nodes, edges = await index_commits(tmp_path, max_commits=10)
    assert len(chunks) == 1
    assert "田中太郎" in chunks[0].metadata["author"]
    assert "機能追加" in chunks[0].content