fix(db): derive rootDir from customDbPath for engine config in openRepo/openReadonlyWithNative

[carlos-alm]

Summary

• openRepo() and openReadonlyWithNative() previously resolved the engine from process.env.CODEGRAPH_ENGINE directly — a process-wide value that ignores the target repo's .codegraphrc.json when customDbPath points to a different repo.
• Now both functions derive rootDir from customDbPath using the established convention (<rootDir>/.codegraph/graph.db) and call loadConfig(rootDir) to get config.build.engine for that repo.
• CODEGRAPH_ENGINE env still wins because applyEnvOverrides() already overwrites config.build.engine when the env var is set.
• opts.engine (explicit CLI flag) still takes precedence in openRepo() via ??.

Test plan

• Full test suite passes (npm test: 3120 tests, 185 files)
• Lint clean (npm run lint)

Closes #1605

[greptile-apps]

Greptile Summary

This PR fixes engine-selection in openRepo and openReadonlyWithNative so each call reads the .codegraphrc.json belonging to the target repository, rather than always resolving config from process.cwd(). The fix derives rootDir from customDbPath/customPath by ascending two directory levels before calling loadConfig(rootDir).

• openRepo: adds rootDir derivation from customDbPath and passes it to loadConfig; opts.engine still takes the highest priority via ??.
• openReadonlyWithNative: same derivation from customPath, mirroring openRepo behavior consistently.
• When neither path is provided, rootDir is undefined and loadConfig(undefined) falls back to process.cwd(), preserving the original behavior.

Confidence Score: 5/5

This is a safe, focused fix that correctly scopes config loading to the target repo's directory in both affected functions.

The change is minimal and well-reasoned: two symmetric two-liner additions, both guarded against undefined input, with a clear fallback to process.cwd() behavior when no path is provided. The priority chain (opts.engine → config.build.engine → 'auto') is unchanged and CODEGRAPH_ENGINE env continues to win via applyEnvOverrides. No error-path regressions are introduced.

No files require special attention.

Important Files Changed

Filename	Overview
src/db/connection.ts	Derives rootDir from customDbPath/customPath via 2-level dirname ascent before calling loadConfig, ensuring the correct per-repo engine config is used instead of always reading the process-level cwd config.

Sequence Diagram

%%{init: {'theme': 'neutral'}}%%
sequenceDiagram
    participant Caller
    participant openRepo/openReadonlyWithNative
    participant loadConfig
    participant fs as .codegraphrc.json

    Caller->>openRepo/openReadonlyWithNative: "customDbPath = "/proj/.codegraph/graph.db""
    openRepo/openReadonlyWithNative->>openRepo/openReadonlyWithNative: "rootDir = dirname(dirname(resolve(customDbPath))) → "/proj""
    openRepo/openReadonlyWithNative->>loadConfig: loadConfig("/proj")
    loadConfig->>fs: read /proj/.codegraphrc.json
    fs-->>loadConfig: "{ build: { engine: "native" } }"
    loadConfig-->>openRepo/openReadonlyWithNative: config
    openRepo/openReadonlyWithNative->>openRepo/openReadonlyWithNative: "engine = opts.engine ?? config.build.engine ?? "auto""
    openRepo/openReadonlyWithNative-->>Caller: "{ repo, close() }"

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sequenceDiagram
    participant Caller
    participant openRepo/openReadonlyWithNative
    participant loadConfig
    participant fs as .codegraphrc.json

    Caller->>openRepo/openReadonlyWithNative: "customDbPath = "/proj/.codegraph/graph.db""
    openRepo/openReadonlyWithNative->>openRepo/openReadonlyWithNative: "rootDir = dirname(dirname(resolve(customDbPath))) → "/proj""
    openRepo/openReadonlyWithNative->>loadConfig: loadConfig("/proj")
    loadConfig->>fs: read /proj/.codegraphrc.json
    fs-->>loadConfig: "{ build: { engine: "native" } }"
    loadConfig-->>openRepo/openReadonlyWithNative: config
    openRepo/openReadonlyWithNative->>openRepo/openReadonlyWithNative: "engine = opts.engine ?? config.build.engine ?? "auto""
    openRepo/openReadonlyWithNative-->>Caller: "{ repo, close() }"

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_{Reviews (2): Last reviewed commit: "fix: resolve merge conflicts with main" | Re-trigger Greptile}

[greptile-apps]

Hardcoded 2-level ascent assumes default dbPath depth

path.dirname(path.dirname(...)) works when customDbPath follows the default <rootDir>/.codegraph/graph.db convention (2 levels deep). If a project has overridden build.dbPath to a shallower or deeper relative path (e.g. "graph.db" at root, or "data/db/graph.db" 3 levels deep), the derived rootDir will point to the wrong directory. loadConfig would then silently return defaults (or even pick up an unrelated config), causing the wrong engine to be selected for that repo. The same pattern appears in openReadonlyWithNative at line 432.

[github-actions]

Codegraph Impact Analysis

2 functions changed → 36 callers affected across 27 files

• openRepo in src/db/connection.ts:370 (28 transitive callers)
• openReadonlyWithNative in src/db/connection.ts:430 (8 transitive callers)