refactor: reduce cyclomatic complexity of computeDeltaModularityDirected

[carlos-alm]

Summary

• computeDeltaModularityDirected (cyc=11, threshold 10) had a documented ||0 asymmetry across its 4 bounds-checked getter call sites, flagged as needing investigation before any unification (risk of masking a real NaN case).
• Confirmed the asymmetry is behaviorally inert: all arrays involved are dense, zero-initialized Float64Arrays, and every value entering them is pre-scrubbed through +x || 0 at ingestion (adapter.ts) — NaN/undefined can never reach these arrays. Cross-checked 3 ways: the same inconsistency exists within computeDeltaCPM on the same array, modularity.ts's independently-written diffModularityDirected reproduces the identical split, and the asymmetry already existed unchanged in the original vendored ngraph.leiden source at the initial vendoring commit.
• Added a shared fgetOrZero helper (documented with this finding), applied uniformly to all 8 reads, and extracted computeDirectedEdgeWeightTerms/computeDirectedStrengthTerms. Cyclomatic 11→3, cognitive 10→2.

Closes #1755

Test plan

• npm test — full suite green (3519 passed, 0 failed)
• npm run lint — clean
• Exact (not approximate) behavior-preservation check: 12 combinations (file/function-level × 3 seeds × 2 resolutions) on this repo's own 701-file/8833-function dependency graph, pre-fix vs. post-fix — byte-for-byte identical quality scores and community assignments, after controlling for an unrelated native-vs-JS-engine resolution difference in the test environment (not a regression)
• New tests pin fgetOrZero's bounds/zero-fill contract and exact-value regression tests for computeDeltaModularityDirected's output

Filed #1871 for an out-of-scope finding: makePartition (cyc=10, pre-existing, unrelated) also exceeds the threshold.

Stacked on #1870 (base branch fix/issue-1754-domain-search-console-log) — only the leiden/test diff is this issue's change.

[greptile-apps]

Greptile Summary

This PR reduces the cyclomatic complexity of computeDeltaModularityDirected (from 11 to 3) by extracting a shared fgetOrZero helper and two private term-computation functions, after thoroughly verifying that the pre-existing || 0 asymmetry across the four read sites was behaviorally inert.

• typed-array-helpers.ts: New fgetOrZero function encapsulates the bounds-check + NaN-guard pattern previously hand-rolled at each call site, with a detailed doc comment explaining both why the guard is safe today and why it's kept for future-proofing.
• partition.ts: computeDirectedEdgeWeightTerms and computeDirectedStrengthTerms replace the four inline ternary reads in computeDeltaModularityDirected; all other callers in the file are untouched.
• leiden.test.ts: Four new unit tests pin fgetOrZero's contract, and two exact floating-point regression tests pin the directed modularity output for both existing directed fixtures.

Confidence Score: 5/5

Clean refactor with no behavioral changes; the extracted helpers and shared accessor directly replace the original hand-rolled ternaries, and exact floating-point regression tests confirm identical output.

The change is purely structural: the formula in computeDeltaModularityDirected is unchanged, the || 0 asymmetry was carefully investigated and confirmed inert, and three independent cross-checks support the author's analysis. New tests pin both the helper contract and exact output values.

No files require special attention.

Important Files Changed

Filename	Overview
src/graph/algorithms/leiden/typed-array-helpers.ts	Adds fgetOrZero: a well-documented bounds-checked accessor that consolidates the scattered pattern; thorough doc comment explains why
src/graph/algorithms/leiden/partition.ts	Extracts computeDirectedEdgeWeightTerms and computeDirectedStrengthTerms helpers to replace the inline bounds-check ternaries in computeDeltaModularityDirected; reduces cyclomatic complexity from 11 to 3 with no behavioral change.
tests/graph/algorithms/leiden.test.ts	Adds unit tests for fgetOrZero covering in-bounds, out-of-bounds, zero-entry, and NaN cases, plus exact floating-point regression tests for computeDeltaModularityDirected output on two graph fixtures.

Flowchart

%%{init: {'theme': 'neutral'}}%%
flowchart TD
    A[computeDeltaModularityDirected] --> B[computeDirectedEdgeWeightTerms]
    A --> C[computeDirectedStrengthTerms]
    B --> D[fgetOrZero inEdgeWeightFromCommunity newC]
    B --> E[fgetOrZero outEdgeWeightToCommunity newC]
    B --> F[fgetOrZero inEdgeWeightFromCommunity oldC]
    B --> G[fgetOrZero outEdgeWeightToCommunity oldC]
    C --> H[fgetOrZero communityTotalInStrength newC]
    C --> I[fgetOrZero communityTotalOutStrength newC]
    C --> J[fgetOrZero communityTotalInStrength oldC]
    C --> K[fgetOrZero communityTotalOutStrength oldC]
    D & E & F & G --> L[deltaInternal]
    H & I & J & K --> M[deltaExpected]
    L & M --> N[return deltaInternal - deltaExpected]

Loading

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flowchart TD
    A[computeDeltaModularityDirected] --> B[computeDirectedEdgeWeightTerms]
    A --> C[computeDirectedStrengthTerms]
    B --> D[fgetOrZero inEdgeWeightFromCommunity newC]
    B --> E[fgetOrZero outEdgeWeightToCommunity newC]
    B --> F[fgetOrZero inEdgeWeightFromCommunity oldC]
    B --> G[fgetOrZero outEdgeWeightToCommunity oldC]
    C --> H[fgetOrZero communityTotalInStrength newC]
    C --> I[fgetOrZero communityTotalOutStrength newC]
    C --> J[fgetOrZero communityTotalInStrength oldC]
    C --> K[fgetOrZero communityTotalOutStrength oldC]
    D & E & F & G --> L[deltaInternal]
    H & I & J & K --> M[deltaExpected]
    L & M --> N[return deltaInternal - deltaExpected]

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_{Reviews (1): Last reviewed commit: "refactor: reduce cyclomatic complexity o..." | Re-trigger Greptile}

[github-actions]

Codegraph Impact Analysis

4 functions changed → 7 callers affected across 2 files

• computeDirectedEdgeWeightTerms in src/graph/algorithms/leiden/partition.ts:268 (4 transitive callers)
• computeDirectedStrengthTerms in src/graph/algorithms/leiden/partition.ts:285 (4 transitive callers)
• computeDeltaModularityDirected in src/graph/algorithms/leiden/partition.ts:303 (4 transitive callers)
• fgetOrZero in src/graph/algorithms/leiden/typed-array-helpers.ts:48 (4 transitive callers)

[carlos-alm]

Recreated as #1925 — this PR was inadvertently closed when its stacked base branch was deleted after #1870 merged. Continuing there.