explore: commitParsedFileOwnedOutline can leave word_index and trigram_index diverged on OOM

[justrach]

Problem

Explorer.commitParsedFileOwnedOutline updates word_index, trigram_index, and outlines in sequence with no atomic rollback. word_index.indexFile calls removeFile first (destructive) before building new entries. If trigram_index.indexFile subsequently fails with OOM, the indexes are left in a split state:

• word_index: has the new content (removeFile + indexFile completed)
• trigram_index: has the old content removed, new content never inserted
• outlines: restored by errdefer to the previous outline

Results: content searches via word_index return results for the new file version, but trigram searches miss the file entirely.

// src/explore.zig — commitParsedFileOwnedOutline
try self.word_index.indexFile(stable_path, content);    // ← removes old first, succeeds
try self.trigram_index.indexFile(stable_path, content); // ← fails OOM: word and trigram now diverged

Fix

Either:

• Re-index word_index on trigram failure (errdefer that re-runs word_index.indexFile with old content)
• Or stage all mutations before committing: compute new trigrams and words without modifying indexes, then apply atomically under lock

[justrach]

Fixed in release/v0.2.57 (commit 6ae58b1). commitParsedFileOwnedOutline now has an errdefer that restores word_index to prior state (re-indexes old content or calls removeFile) if trigram_index.indexFile fails.