fix: correct blast-radius/fn-impact computation for line-shifted declarations on incremental rebuild

[carlos-alm]

Summary

• reconnectReverseDepEdges/reconnect_reverse_dep_edges re-attach a reverse-dep caller's edge to its purged-and-reinserted target using (name, kind, file) plus nearest-old-line as a tiebreak. When unrelated code shifts a whole group of same-named/same-kind siblings (e.g. connection.ts has four object-literal close() {} methods), an old reference line can end up numerically closer to the wrong sibling's new line, silently reattaching the edge to it — losing edges on one sibling while duplicating them on another.
• checkMaxBlastRadius/fnImpactData are pure node-ID graph traversal with no line-keyed logic — confirmed the defect is entirely upstream in edge reconnection, no interaction with titan-gate: flat blast-radius threshold false-positives on additive-only changes to high-fan-in core functions #1740's diff-handling changes in the same file.
• Fixed by recording each target's 1-based ordinal rank among same-(name,kind) siblings before purge (computeNodeOrdinals/compute_ordinals), and reconnecting using that saved ordinal instead of line proximity (pickReconnectTarget/pick_reconnect_target), falling back to nearest-line only if the sibling count itself changed.

Closes #1752

Test plan

• npm test — full suite green (3502 passed, 0 failed)
• npm run lint — clean
• cargo test --release — 443 passed
• Native addon rebuilt, codesigned, verified directly
• A/B proof on both engines: reverted to pre-fix source, rebuilt, reproduced the exact bug signature; restored fix, reconfirmed pass
• Scenario matrix: 3 shift positions × 4 touched-sibling variants × 2 engines = 24 combinations, all pass against full-rebuild ground truth
• 5 repeated cycles + a 3-step chained incremental sequence (no full rebuild in between) — stable

Filed #1865 for a genuinely separate, pre-existing (not a regression) gap found during stress-testing: when a same-named/same-kind sibling is also added or removed in the same edit that shifts the group, the ordinal-based fix's own line-proximity fallback still diverges from a full rebuild — suggests per-declaration content hashing as the fix.

Stacked on #1862 (base branch fix/issue-1751-closedbpair-test-coverage) — only the builder/detect-changes/test diff is this issue's change.

[greptile-apps]

Greptile Summary

This PR fixes a silent edge-mismatch bug in incremental rebuild: when multiple nodes in a file share the same name and kind (e.g. four close() {} methods in connection.ts), the old nearest-line heuristic could reconnect a saved reverse-dep edge to the wrong sibling after a purge-and-reinsert cycle shifted the whole group. The fix records each target's 1-based ordinal rank among same-(name,kind) siblings before purge and uses that ordinal — not line proximity — to reselect the correct candidate after reinsertion.

• Both engines updated in lockstep: detect-changes.ts + build-edges.ts (WASM/JS) and detect_changes.rs (native) receive identical computeNodeOrdinals/pickReconnectTarget logic, so the fix applies regardless of which engine is active.
• Candidate-list caching added: reconnectReverseDepEdges and reconnect_reverse_dep_edges now cache the SELECT id, line FROM nodes … query result per (name, kind, file) group, avoiding redundant DB round-trips when multiple callers share a target.
• Test coverage: Four Rust unit tests cover pick_reconnect_target and compute_ordinals in isolation, plus a full end-to-end Rust integration test and a WASM-path integration test (issue-1752-reverse-dep-sibling-reconnect.test.ts) that replays the exact real-world bug shape against a fresh full-rebuild ground truth.

Confidence Score: 5/5

Safe to merge — the fix is self-contained, both engines are updated in lockstep, and the change introduces no new failure modes on the hot path.

The ordinal-rank approach is algorithmically sound: ordinals are computed from the pre-purge DB snapshot, candidates are queried post-reinsert with the same ascending-line sort, and the index arithmetic is straightforward. Both the TypeScript (WASM) and Rust (native) implementations are structurally identical and verified against each other. The known remaining gap (sibling count changes) is explicitly documented, filed as #1865, and handled gracefully via the nearest-line fallback rather than silently corrupting data. Test coverage is thorough: four focused Rust unit tests, one Rust end-to-end integration test, and one WASM integration test that compares against a fresh full-rebuild ground truth — exactly the right shape for catching regressions in this area.

No files require special attention.

Important Files Changed

Filename	Overview
crates/codegraph-core/src/domain/graph/builder/stages/detect_changes.rs	Adds compute_ordinals, pick_reconnect_target, and updates save/reconnect functions with ordinal-based logic and candidate caching; comprehensive unit + integration tests included.
src/domain/graph/builder/stages/detect-changes.ts	Adds computeNodeOrdinals and wires tgtOrdinal/tgtSiblingCount into savedReverseDepEdges before purge; mirrors the Rust implementation faithfully.
src/domain/graph/builder/stages/build-edges.ts	Adds pickReconnectTarget and refactors reconnectReverseDepEdges to use ordinal-based selection with a per-group candidate cache; logic is correct and consistent with the Rust mirror.
src/domain/graph/builder/context.ts	Adds tgtOrdinal and tgtSiblingCount fields to the SavedReverseDepEdge interface; straightforward type update.
tests/integration/issue-1752-reverse-dep-sibling-reconnect.test.ts	New WASM-path regression test that builds incrementally, then compares target lines against an independent full-rebuild reference; also guards against the edge-collapsing variant of the bug.

Sequence Diagram

%%{init: {'theme': 'neutral'}}%%
sequenceDiagram
    participant D as detect-changes / detect_changes.rs
    participant DB as SQLite (graph.db)
    participant B as build-edges / reconnect fn

    Note over D,DB: Incremental rebuild — changed file detected

    D->>DB: "computeNodeOrdinals(file)<br/>SELECT name, kind, line FROM nodes WHERE file=?"
    DB-->>D: rows (pre-purge snapshot)
    Note over D: Group by (name,kind), sort by line,<br/>assign 1-based ordinals

    D->>DB: saveEdgesStmt: SELECT reverse-dep edges for file
    DB-->>D: rows with source_id, tgt_name, tgt_kind, tgt_line, …
    Note over D: Attach tgtOrdinal + tgtSiblingCount<br/>from ordinals map → savedReverseDepEdges

    D->>DB: "purge: DELETE nodes WHERE file=?<br/>(and their edges)"

    D->>DB: re-insert updated nodes (new IDs, shifted lines)

    B->>DB: "candidatesStmt: SELECT id, line FROM nodes<br/>WHERE name=? AND kind=? AND file=? ORDER BY line"
    DB-->>B: candidates list (post-reinsert, cached per group)

    Note over B: pickReconnectTarget:<br/>if count unchanged → use saved ordinal<br/>else → nearest-line fallback

    B->>DB: INSERT OR IGNORE INTO edges (source_id, new_target_id, …)
    Note over B: Edge reconnected to the CORRECT sibling

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sequenceDiagram
    participant D as detect-changes / detect_changes.rs
    participant DB as SQLite (graph.db)
    participant B as build-edges / reconnect fn

    Note over D,DB: Incremental rebuild — changed file detected

    D->>DB: "computeNodeOrdinals(file)<br/>SELECT name, kind, line FROM nodes WHERE file=?"
    DB-->>D: rows (pre-purge snapshot)
    Note over D: Group by (name,kind), sort by line,<br/>assign 1-based ordinals

    D->>DB: saveEdgesStmt: SELECT reverse-dep edges for file
    DB-->>D: rows with source_id, tgt_name, tgt_kind, tgt_line, …
    Note over D: Attach tgtOrdinal + tgtSiblingCount<br/>from ordinals map → savedReverseDepEdges

    D->>DB: "purge: DELETE nodes WHERE file=?<br/>(and their edges)"

    D->>DB: re-insert updated nodes (new IDs, shifted lines)

    B->>DB: "candidatesStmt: SELECT id, line FROM nodes<br/>WHERE name=? AND kind=? AND file=? ORDER BY line"
    DB-->>B: candidates list (post-reinsert, cached per group)

    Note over B: pickReconnectTarget:<br/>if count unchanged → use saved ordinal<br/>else → nearest-line fallback

    B->>DB: INSERT OR IGNORE INTO edges (source_id, new_target_id, …)
    Note over B: Edge reconnected to the CORRECT sibling

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_{Reviews (1): Last reviewed commit: "fix: correct blast-radius/fn-impact comp..." | Re-trigger Greptile}

[github-actions]

Codegraph Impact Analysis

5 functions changed → 12 callers affected across 5 files

• PipelineContext in src/domain/graph/builder/context.ts:21 (4 transitive callers)
• pickReconnectTarget in src/domain/graph/builder/stages/build-edges.ts:1991 (3 transitive callers)
• reconnectReverseDepEdges in src/domain/graph/builder/stages/build-edges.ts:2024 (3 transitive callers)
• computeNodeOrdinals in src/domain/graph/builder/stages/detect-changes.ts:395 (4 transitive callers)
• addReverseDeps in src/domain/graph/builder/stages/detect-changes.ts:438 (4 transitive callers)

[carlos-alm]

Recreated as #1916 — this PR was inadvertently closed when its stacked base branch was deleted after #1910 merged. Continuing there.