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>

src/extraction/index.ts

@@ -116,6 +116,20 @@ export interface SyncResult {
   nodesUpdated: number;
   durationMs: number;
   changedFilePaths?: string[];
+  /**
+   * Symbol names whose set of definitions this sync CHANGED — names the synced
+   * files gained or lost, as the symmetric difference of their `file\0name`
+   * definition pairs before and after the store phase (per file, so a name
+   * moving between two changed files does not cancel itself out).
+   * Resolution picks among all same-named definitions project-wide,
+   * so these are exactly the names whose already-resolved edges — in files this
+   * sync never touched — may now bind elsewhere and must be re-resolved for the
+   * index to stay convergent with a full rebuild (CG-33).
+   *
+   * A body-only edit leaves this empty, which is the common case and costs
+   * nothing downstream.
+   */
+  definitionDelta?: string[];
 }
 
 /**
@@ -2491,6 +2505,64 @@ export class ExtractionOrchestrator {
     }
   }
 
+  /**
+   * Re-open, for re-resolution, every resolution edge whose answer this sync
+   * may have changed — the fix for index drift (CG-33).
+   *
+   * Incremental sync re-resolves only the references IN the changed files, but
+   * resolution's answer is a function of the WHOLE graph: a reference binds to
+   * one of the same-named definitions project-wide, so adding or removing a
+   * definition of `pct` can change which `pct` every other file's `pct(...)`
+   * should bind to. Those other files are never revisited, and their references
+   * resolved successfully once and were deleted from `unresolved_refs`, so
+   * nothing existed to revisit them with — the index kept an answer that was
+   * correct against an older graph. Measured on codegraph's own long-lived
+   * index: 4.3% of distinct edges differed from a clean rebuild, in BOTH
+   * directions, overwhelmingly `calls`. See docs/benchmarks/index-drift-cg33.md.
+   *
+   * This deletes each affected edge and re-inserts it as the reference that
+   * created it (the refName/refKind stamp), status='pending', for the sync's
+   * resolution sweep to bind against the post-sync graph — the same input a
+   * full rebuild resolves from, which is what makes the two converge.
+   *
+   * Deliberately conservative in three ways, because a wrong deletion is a
+   * permanent edge loss while a missed rebind is only residual drift:
+   * - an edge with no refName stamp (synthesized, or built by an engine older
+   *   than the stamp) is left ALONE rather than reconstructed from the target's
+   *   plain name, same rule as `resurrectRefFromDroppedEdge`;
+   * - edges whose source is in a file this sync already re-extracted are
+   *   skipped — their references were re-resolved from scratch moments ago;
+   * - very common names are skipped by the per-name ceiling in
+   *   `getResolutionEdgesByTargetName`.
+   *
+   * Returns the number of references resurrected.
+   */
+  resurrectStaleResolutionEdges(definitionDelta: string[], changedFilePaths: string[]): number {
+    if (definitionDelta.length === 0) return 0;
+    const alreadyFresh = new Set(changedFilePaths);
+    const candidates = this.queries.getResolutionEdgesByTargetName(definitionDelta);
+
+    const edgeIds: number[] = [];
+    const refs: UnresolvedReference[] = [];
+    for (const e of candidates) {
+      if (alreadyFresh.has(e.sourceFilePath)) continue;
+      const ref = resurrectRefFromDroppedEdge(e);
+      if (!ref) continue; // no stamp — never delete what we cannot restore
+      edgeIds.push(e.edgeId);
+      refs.push(ref);
+    }
+    if (refs.length === 0) return 0;
+
+    // Delete first. The sweep re-inserts whichever edge resolution now picks,
+    // and `insertEdges` is INSERT OR IGNORE against idx_edges_identity — so a
+    // rebind to the same target is a clean no-op, but leaving the old row in
+    // place for a rebind ELSEWHERE would keep both, turning drift into
+    // duplication.
+    this.queries.deleteEdgesByIds(edgeIds);
+    this.queries.insertUnresolvedRefsBatch(refs);
+    return refs.length;
+  }
+
   /**
    * Sync the index with the current file state.
    *
@@ -2520,6 +2592,10 @@ export class ExtractionOrchestrator {
     let filesRemoved = 0;
     let nodesUpdated = 0;
     const changedFilePaths: string[] = [];
+    // `file\0name` definition pairs for the files this sync touches, sampled
+    // BEFORE their nodes are replaced/deleted. Compared against the post-store
+    // pairs below to derive `definitionDelta` (CG-33).
+    const pairsBefore = new Set<string>();
 
     onProgress?.({
       phase: 'scanning',
@@ -2585,6 +2661,9 @@ export class ExtractionOrchestrator {
         // failed until the symbol reappears somewhere. (A deleted file whose
         // CALLERS are also being deleted is fine: their nodes cascade later
         // in this loop and take the resurrected rows with them.)
+        // Every name this file defined is about to stop existing here, which
+        // narrows the candidate set for that name repo-wide (CG-33).
+        for (const pair of this.queries.getNodeNamePairsByFiles([tracked.path])) pairsBefore.add(pair);
         const incoming = this.queries.getCrossFileIncomingEdgesWithTarget(tracked.path);
         if (incoming.length > 0) {
           const resurrected = incoming
@@ -2651,6 +2730,14 @@ export class ExtractionOrchestrator {
       }
     }
 
+    // Sampled here — after the add/modify classification, before any file is
+    // re-extracted — because `storeExtractionResult` deletes a file's nodes
+    // before inserting the new ones, so this is the last point the pre-edit
+    // definition set is readable (CG-33).
+    if (filesToIndex.length > 0) {
+      for (const pair of this.queries.getNodeNamePairsByFiles(filesToIndex)) pairsBefore.add(pair);
+    }
+
     // Load only grammars needed for changed files
     if (filesToIndex.length > 0) {
       const overrides = loadExtensionOverrides(this.rootDir);
@@ -2677,6 +2764,25 @@ export class ExtractionOrchestrator {
       nodesUpdated += result.nodes.length;
     }
 
+    // Names whose definition set this sync changed: a `file\0name` pair present
+    // before but not after (removed/renamed away) or after but not before
+    // (added). A pair on both sides is untouched as far as resolution's
+    // candidate set is concerned — only its node id moved, which
+    // reattachCrossFileEdges already follows — so an edit that only changes
+    // bodies yields an empty delta and no downstream rebind work (CG-33).
+    //
+    // Compared per FILE, not as one name set over the whole batch: a commit
+    // that adds `collect` to a new file while an unrelated changed file already
+    // defined `collect` must still flag the name, and a bare name set cancels
+    // exactly that case out. That miss left the largest residual class in the
+    // first measurement of this fix.
+    const pairsAfter = this.queries.getNodeNamePairsByFiles(filesToIndex);
+    const deltaNames = new Set<string>();
+    const nameOf = (pair: string) => pair.slice(pair.indexOf('\0') + 1);
+    for (const pair of pairsBefore) if (!pairsAfter.has(pair)) deltaNames.add(nameOf(pair));
+    for (const pair of pairsAfter) if (!pairsBefore.has(pair)) deltaNames.add(nameOf(pair));
+    const definitionDelta = [...deltaNames];
+
     return {
       filesChecked,
       filesAdded,
@@ -2685,6 +2791,7 @@ export class ExtractionOrchestrator {
       nodesUpdated,
       durationMs: Date.now() - startTime,
       changedFilePaths: changedFilePaths.length > 0 ? changedFilePaths : undefined,
+      definitionDelta: definitionDelta.length > 0 ? definitionDelta : undefined,
     };
   }