feat(agent-runtime): add indexed candidate verification for code search

[yacosta738]

Use the workspace trigram index only to narrow candidate files, then verify matches against live file contents for deterministic and correct results.

This pull request adds a new candidate planning system to the search index, enabling efficient and accurate selection of search candidate files based on query patterns and index coverage. It introduces new types and logic to assess index completeness, filter candidates using trigrams, and determine when the index is stale or insufficient. The PR also provides comprehensive tests for these features.

Candidate Planning and Index Coverage:

• Added CandidateCoverage, CandidateRequest, and CandidatePlan types to represent candidate search planning and index coverage status in WorkspaceTrigramIndex.
• Implemented plan_candidates method in WorkspaceTrigramIndex to plan candidate search files, check for required trigrams, intersect with discovered files, and classify coverage as complete, partial, or unavailable.
• Added helper functions normalized_relative_root and extract_required_trigrams for processing search requests and extracting trigrams.

Database Query Enhancements:

• Added read_candidate_paths and read_index_file_count to sqlite.rs for efficiently querying candidate file paths matching required trigrams and counting indexed files.

Testing and API Exposure:

• Exposed new types and methods in the module API, and added extensive tests covering candidate planning, index coverage classification, and candidate path selection. [1] [2]

Other:

• Minor import and dependency updates to support the new functionality. [1] [2] [3]

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ℹ️ Review info

⚙️ Run configuration

Configuration used: Path: .coderabbit.yaml

Review profile: ASSERTIVE

Plan: Pro

Run ID: a896f78b-4ae4-4669-959d-24229a72b52c

📥 Commits

Reviewing files that changed from the base of the PR and between 024aa20 and 42c01f5.

📒 Files selected for processing (18)

• clients/agent-runtime/src/search/index.rs
• clients/agent-runtime/src/search/mod.rs
• clients/agent-runtime/src/search/sqlite.rs
• clients/agent-runtime/src/search/tests.rs
• clients/agent-runtime/src/tools/code_search.rs
• openspec/changes/archive/2026-04-05-indexed-candidate-selection/design.md
• openspec/changes/archive/2026-04-05-indexed-candidate-selection/proposal.md
• openspec/changes/archive/2026-04-05-indexed-candidate-selection/specs/regex-semantics/spec.md
• openspec/changes/archive/2026-04-05-indexed-candidate-selection/specs/result-format/spec.md
• openspec/changes/archive/2026-04-05-indexed-candidate-selection/specs/safety-model/spec.md
• openspec/changes/archive/2026-04-05-indexed-candidate-selection/specs/workspace-index/spec.md
• openspec/changes/archive/2026-04-05-indexed-candidate-selection/state.yaml
• openspec/changes/archive/2026-04-05-indexed-candidate-selection/tasks.md
• openspec/changes/archive/2026-04-05-indexed-candidate-selection/verify-report.md
• openspec/specs/regex-semantics/spec.md
• openspec/specs/result-format/spec.md
• openspec/specs/safety-model/spec.md
• openspec/specs/workspace-index/spec.md

✨ Finishing Touches

🧪 Generate unit tests (beta)

• Create PR with unit tests
• Commit unit tests in branch feat/indexed-candidate-selection

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[github-actions]

✅ Contributor Report

User: @yacosta738
Status: Passed (12/13 metrics passed)

Metric	Description	Value	Threshold	Status
PR Merge Rate	PRs merged vs closed	89%	>= 30%	✅
Repo Quality	Repos with ≥100 stars	0	>= 0	✅
Positive Reactions	Positive reactions received	10	>= 1	✅
Negative Reactions	Negative reactions received	0	<= 5	✅
Account Age	GitHub account age	3082 days	>= 30 days	✅
Activity Consistency	Regular activity over time	108%	>= 0%	✅
Issue Engagement	Issues with community engagement	0	>= 0	✅
Code Reviews	Code reviews given to others	515	>= 0	✅
Merger Diversity	Unique maintainers who merged PRs	2	>= 0	✅
Repo History Merge Rate	Merge rate in this repo	90%	>= 0%	✅
Repo History Min PRs	Previous PRs in this repo	200	>= 0	✅
Profile Completeness	Profile richness (bio, followers)	90	>= 0	✅
Suspicious Patterns	Spam-like activity detection	1	N/A	❌

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_{Contributor Report evaluates based on public GitHub activity. Analysis period: 2025-04-05 to 2026-04-05}

[sonarqubecloud]

Quality Gate passed

Issues
0 New issues
0 Accepted issues

Measures
0 Security Hotspots
92.7% Coverage on New Code
0.0% Duplication on New Code

See analysis details on SonarQube Cloud