fix(watch): report net edge delta not gross re-inserted count

[carlos-alm]

Summary

• Track outgoing edge count per file before purgeFileData (edgesBefore in IncrementalStmts + RebuildResult)
• logRebuildResults now shows edgesAdded - edgesBefore so a no-op save reports +0 edges instead of e.g. +10 edges
• Negative values (edges removed) are now surfaced correctly as -N edges

Test plan

• Existing watcher integration tests pass (watcher-fk-embeddings, watcher-rebuild)
• Full test suite green (159 files, 2771 tests)
• Manual: start codegraph watch, edit a file without changing imports/calls → log shows +0 edges

Closes #1241

[greptile-apps]

Greptile Summary

This PR fixes the edge-delta reporting in the incremental watcher by capturing outgoing edge counts before purgeFileData and before each reverse-dep's deleteOutgoingEdges, then computing edgesAdded - edgesBefore (net delta) rather than the raw gross re-inserted count. Both the human-facing log and the machine-readable change event journal now use the net delta.

• IncrementalStmts gains a countEdges prepared statement; RebuildResult gains edgesBefore; both are wired through buildDeletionResult, the fileNodeRow-null early return, and the main rebuild path.
• parseReverseDeps now accumulates reverseDepsEdgesBefore (summed before each deleteOutgoingEdges call) and returns it up through runReverseDepCascade → rebuildFile, which adds it to the target file's edgesBefore so the net delta is accurate even when a shared utility file is saved and triggers a reverse-dep cascade.
• Both integration test fixtures (watcher-fk-embeddings, watcher-rebuild) receive the new countEdges statement so their makeStmts helpers remain in sync with the updated IncrementalStmts interface.

Confidence Score: 5/5

Safe to merge — the fix is logically complete across all rebuild paths including deletion, early returns, and reverse-dep cascades.

The edge-counting logic correctly captures baselines before each deletion step (purgeFileData for the target file, deleteOutgoingEdges for each reverse dep), sums them into totalEdgesBefore, and both the log and change event journal now report the true net delta. All four changed files are narrow and coherent. The previous reviewer concern about reverse-dep cascade inflation is addressed in commit b5bb5d1 and the fix is present in this diff.

No files require special attention.

Important Files Changed

Filename	Overview
src/domain/graph/builder/incremental.ts	Core fix: adds countEdges to IncrementalStmts, captures edgesBefore for the target file and each reverse dep before deletion, and threads totalEdgesBefore through RebuildResult. Logic is sound across all code paths (deletion, fileNodeRow-null early return, and normal rebuild with cascade).
src/domain/graph/watcher.ts	Watcher correctly updated: countEdges statement added, local RebuildResult gains edgesBefore, both logRebuildResults and buildChangeEvent now use the net delta (edgesAdded - edgesBefore). Addresses both the log and the change event journal.
tests/integration/watcher-fk-embeddings.test.ts	Test fixture makeStmts updated to include countEdges prepared statement, keeping it in sync with the updated IncrementalStmts interface.
tests/integration/watcher-rebuild.test.ts	Test fixture makeStmts updated to include countEdges prepared statement, keeping it in sync with the updated IncrementalStmts interface.

Flowchart

%%{init: {'theme': 'neutral'}}%%
flowchart TD
    A[rebuildFile called] --> B[countEdges for target file → edgesBefore]
    B --> C[findReverseDeps]
    C --> D[purgeFileData — deletes target edges & nodes]
    D --> E{file still exists?}
    E -- No --> F[buildDeletionResult\nedgesAdded=0, edgesBefore=edgesBefore\nnet delta = -edgesBefore]
    E -- Yes --> G[parseFileIncremental]
    G --> H{fileNodeRow exists?}
    H -- No --> I[early return\nedgesAdded=0, edgesBefore=edgesBefore]
    H -- Yes --> J[rebuildEdgesForTargetFile → edgesAdded]
    J --> K[runReverseDepCascade]
    K --> L[parseReverseDeps loop\nfor each dep: countEdges → reverseDepsEdgesBefore\nthen deleteOutgoingEdges]
    L --> M[rebuild dep edges → cascadeEdges]
    M --> N[totalEdgesBefore = edgesBefore + reverseDepsEdgesBefore\ntotal edgesAdded = edgesAdded + cascadeEdges]
    N --> O[RebuildResult\nnet delta = edgesAdded − totalEdgesBefore]
    O --> P[logRebuildResults: edgeDelta display]
    O --> Q[buildChangeEvent: edgesAdded = net delta]

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_{Reviews (5): Last reviewed commit: "Merge branch 'main' into fix/watch-net-e..." | Re-trigger Greptile}

[greptile-apps]

Reverse-dep cascade inflates edgesAdded vs edgesBefore

edgesBefore counts only outgoing edges from the target file, but edgesAdded is the sum of target-file edges and all re-inserted reverse-dep edges (via runReverseDepCascade). Each reverse dep has its old outgoing edges deleted by deleteOutgoingEdges then re-inserted, so their count lands entirely in edgesAdded with no corresponding offset in edgesBefore.

Concretely, editing a shared utility file (e.g. utils.ts) imported by 3 other files where each dep has 5 edges: edgesBefore = 10, edgesAdded = 10 + 15 = 25, reported delta = +15 — not +0 as the test plan states. The "+0 for a no-op save" guarantee only holds for leaf files (no reverse deps).

[carlos-alm]

Fixed — parseReverseDeps now counts each reverse dep's outgoing edges (via stmts.countEdges) before calling deleteOutgoingEdges, and returns the total as reverseDepsEdgesBefore. runReverseDepCascade now returns { edgesAdded, reverseDepsEdgesBefore } and rebuildFile adds reverseDepsEdgesBefore to edgesBefore so the net delta (edgesAdded - edgesBefore) is correct for files with any number of reverse deps. Commit b5bb5d1.

[carlos-alm]

Addressed Greptile's review feedback:

Issue 1 — reverse-dep cascade inflates edgesAdded vs edgesBefore (inline comment on incremental.ts:693):

• parseReverseDeps now queries stmts.countEdges for each dep before calling deleteOutgoingEdges, accumulating the total in reverseDepsEdgesBefore
• runReverseDepCascade returns { edgesAdded, reverseDepsEdgesBefore }
• rebuildFile computes totalEdgesBefore = edgesBefore + reverseDepsEdgesBefore, so the net delta is correct for shared files with any number of reverse deps

Issue 2 — edgesAdded in change event vs net delta in log (review body comment on watcher.ts:110-116):

• buildChangeEvent now receives r.edgesAdded - r.edgesBefore (the net delta) instead of the gross count, keeping the change journal consistent with the log output

[carlos-alm]

@greptileai

[github-actions]

Codegraph Impact Analysis

10 functions changed → 9 callers affected across 3 files

• IncrementalStmts.countEdges in src/domain/graph/builder/incremental.ts:33 (0 transitive callers)
• RebuildResult.edgesBefore in src/domain/graph/builder/incremental.ts:44 (0 transitive callers)
• buildDeletionResult in src/domain/graph/builder/incremental.ts:517 (3 transitive callers)
• parseReverseDeps in src/domain/graph/builder/incremental.ts:564 (3 transitive callers)
• runReverseDepCascade in src/domain/graph/builder/incremental.ts:622 (3 transitive callers)
• rebuildFile in src/domain/graph/builder/incremental.ts:652 (4 transitive callers)
• prepareWatcherStatements in src/domain/graph/watcher.ts:18 (3 transitive callers)
• RebuildResult.edgesBefore in src/domain/graph/watcher.ts:58 (0 transitive callers)
• writeJournalAndChangeEvents in src/domain/graph/watcher.ts:99 (4 transitive callers)
• logRebuildResults in src/domain/graph/watcher.ts:125 (4 transitive callers)