CG-33: converge incremental sync with a full rebuild

A live, auto-synced index did not converge to a clean rebuild of the same
tree — 4.3% of distinct edges wrong in both directions on this repo's own
index, overwhelmingly `calls`, which is what flow queries traverse and what
explore's file ranking weights. Silent: nothing warned, and the symptom read
as "codegraph isn't very good" rather than "this index needs rebuilding."

Two causes, and the fix needed both. Resolution binds a reference to one of
the same-named definitions PROJECT-WIDE, so a definition appearing or
vanishing changes the correct answer for references in files the sync never
touches — and those references resolved successfully once, which deletes
their unresolved_refs row, leaving nothing to revisit them with (#1240's
retry only revisits refs parked as failed). Separately, when nothing
disambiguated the candidates the winner came down to rowid, i.e. the order
files happened to be WRITTEN, which differs between a scan-order full index
and a sync that appends each file as it changes. That second one is why
re-resolution alone could not converge: re-resolving against the identical
graph still picked a different candidate.

So getNodesByName now orders by (file_path, start_line) — a property of the
code, not of the write order — and sync computes a definitionDelta and
re-opens the resolution edges whose answer it may have invalidated,
re-inserting each as the reference that created it for the orphan sweep to
bind against the post-sync graph.

The delta compares `file\0name` pairs per file rather than one name set over
the batch: a commit that adds `collect` to a new file while an unrelated
changed file already defines `collect` cancels out of a batch-wide set, and
that miss was the largest residual class in the first measurement.

Conservative where the failure modes are asymmetric — a wrong deletion is a
permanent edge loss, a missed rebind is only residual drift. Edges without a
refName stamp are never touched (nothing to restore them from), sources the
sync already re-extracted are skipped, and a per-name ceiling declines the
generic names. Edges are deleted before the sweep re-inserts, since
INSERT OR IGNORE against idx_edges_identity would otherwise keep both rows
when a reference rebinds elsewhere.

Replaying real commits of this repo through sync, then diffing against a
rebuild: 16 commits 48 -> 0; 80 commits 1,634 -> 361, with the actively
misleading direction (stale edges the index keeps asserting) 671 -> 2.
Index and sync wall-clock are unchanged; the ORDER BY costs 18% per uncached
name lookup, which never reaches wall-clock because the resolver memoizes it.

The 357-edge residual at 80 commits is one pre-existing class: refs to
generic names (`push`, `join`) parked above #1240's per-name retry ceiling,
which a rebuild resolves into cross-language garbage — a TS test file
"calling" an R method. Converging there would mean manufacturing wrong edges,
so it is left alone. And no drift metric in `codegraph status`: it cannot be
computed without the rebuild it would be recommending, and a proxy would fire
on that residual and train users to ignore it.

Co-Authored-By: Claude Opus 5 <noreply@anthropic.com>

CHANGELOG.md

@@ -17,6 +17,7 @@ and adheres to [Semantic Versioning](https://semver.org/spec/v2.0.0.html).
 
 ### Fixes
 
+- A long-lived index no longer drifts away from what a fresh `codegraph index` would produce. When a file gained or lost a symbol, references to that name in files the sync never touched kept pointing at the definition that was correct before the change, and — because nothing distinguished two same-named definitions — the winner could come down to the order files happened to be written, which differs between a full index and a sync. On this project's own repository, replaying 80 commits through `sync` left 5.7% of connections wrong; it is now 1.3%, and the wrong-answers-still-being-asserted half drops by 99.7%. Since call edges are what flow questions follow and what `codegraph_explore` ranks files by, this quietly degraded answers as an index aged, with nothing to indicate it. Syncing is unchanged in speed, and an edit that only changes a function's body does no extra work at all. Set `CODEGRAPH_NO_REBIND=1` to opt out.
 - `codegraph_explore` now concentrates its answer on the code that actually answers your question instead of spreading it across files that merely share a word with it, so more of the answer arrives in a single call. Thanks @LeDuyViet for the detailed measurements and reproduction. (#1500)
 - Files only weakly related to your question now come back as a name, symbol and line number instead of spending the answer on their source — name one of them in a follow-up `codegraph_explore` to get it back in full. (#1500)
 - A generated CRUD or protobuf layer no longer crowds out the hand-written code sitting beside it: generated files are now recognized by the `// Code generated by … DO NOT EDIT.` style banner written at the top of the file, not just by a filename that looks generated. Re-index after upgrading to pick up the new detection. (#1500)