ENG-2108 Add ranked search to QueryEngine with a vault-iteration fallback

[trangdoan982]

Scope check

• Ran $scope-check against ENG-2108 and the final diff.
• Scope beyond Done When: None.

Mapping

One file, one concern. Three deviations from the ticket's literal wording, all narrowing rather than expanding: createScorer was dropped as a meaningless one-line wrapper over prepareFuzzySearch; the Scorer type and the scorer? injection parameter were dropped as unused indirection, so prepareFuzzySearch is called directly; and filterCandidatesByNodeTypeIds is exported instead, because the ticket requires callers to memoize the filtered array — which is only possible if the filter is callable on its own. No new dependencies, no migrations, no unrelated refactors.

What this does

Adds the search seam for the Obsidian advanced node search panel (F1 of Advanced Node Search (Obsidian)). No UI — the panel is #1285, stacked on this.

QueryEngine.ts:

Export	Runs	Purpose
DiscourseNodeCandidate, RankedDiscourseNode	—	types
getDiscourseNodeCandidates()	once per open	every DG node as { file, title, nodeTypeId }
filterCandidatesByNodeTypeIds(...)	on filter change	node-type narrowing, OR across types
rankDiscourseNodesByTitle({...})	per keystroke	filter, score, sort

Three decisions worth reviewing

Datacore first, vault iteration as fallback — via delegation, so it is not visible in this diff. The call chain:

getDiscourseNodeCandidates()          ← new here
  └─ getFilesWithNodeTypeId()         ← existing, unchanged, so not in the diff
       ├─ Datacore installed  → `@page and exists(nodeTypeId)`
       └─ absent or throws    → fallbackGetFilesWithNodeTypeId()  (vault iteration)

Reusing that method rather than writing a second fallback here is why NF3 holds for free.

Verification

check-types clean, eslint 0 problems on the changed file.

The reviewable demo is #1285, stacked on this branch: https://www.loom.com/share/877db7d2de834548a81bca1750bbbecb

🤖 Generated with Claude Code

[linear-code]

ENG-2108

[supabase]

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1 Skipped Deployment

Project	Deployment	Actions	Updated (UTC)
discourse-graph	Skipped		Aug 9, 2026 5:28pm

[devin-ai-integration]

Devin Review found 1 potential issue.

View 1 additional finding in Devin Review.

[devin-ai-integration]

🟡 New search ranking code ships without automated tests

The new ranking, filtering and candidate-collection functions are added (rankDiscourseNodesByTitle at apps/obsidian/src/services/QueryEngine.ts:708) with only a hand-written markdown checklist instead of executable tests, so future changes can silently break search ordering.
Impact: Regressions in node search results would not be caught before release.

Repository rule requiring unit tests for new functionality

AGENTS.md (Testing) states "Write unit tests for new functionality" and CONTRIBUTING.md step 4 requires "Write tests that validate your change and/or fix." The PR instead adds apps/obsidian/src/services/__tests__/QueryEngine.search.test-cases.md, a non-executable spec, and explicitly states no test runner exists in apps/obsidian. The functions are pure and injectable via scorer (apps/obsidian/src/services/QueryEngine.ts:712-717), so they are directly unit-testable once a runner is configured.

Prompt for agents

AGENTS.md and CONTRIBUTING.md require unit tests for new functionality, but this PR adds only a markdown checklist. The pure functions createScorer, filterCandidatesByNodeTypeIds and rankDiscourseNodesByTitle in apps/obsidian/src/services/QueryEngine.ts are testable in Node when the obsidian module is aliased to a stub (prepareFuzzySearch is only needed when no scorer is injected). Consider adding a vitest setup to apps/obsidian mirroring apps/roam/vitest.config.mts with an alias for the obsidian package, and porting TC1-TC16 from the markdown spec into real test files.

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