perf(resolution): fix O(K²) import-node blowup in "Resolving refs" (#915) (#965)

* perf(resolution): resolve imports to definitions, not sibling import nodes (#915)

"Resolving refs" crawled (tens of minutes) on large projects — most painfully
ones mixing a big front-end and back-end. An external package or module imported
across hundreds/thousands of files (react, a shared UI package, Python
logging/typing) is re-declared as an `import` node in every importing file, so
its unresolved import ref fell through to the exact-name matcher, which scored
all K same-named import nodes via findBestMatch — K refs x K candidates = O(K^2)
per package, producing only meaningless import->import edges.

Fix: exclude `import`-kind nodes as name-match targets (they're statements, not
definitions; real import->definition resolution is the import resolver's job).
Plus two safe constant-factor wins in findBestMatch: hoist the per-candidate
ref.filePath split, and skip cross-language candidates when a same-language one
exists (provably the same winner — same-language scores >=50, cross-language
maxes at 35).

Measured: superset (Py+TS) candidates scored 7.5M -> 833K (9x), non-import edges
preserved (+1618 now resolve to real defs), ~22K useless import->import edges
removed; kubernetes (Go) computePathProximity 37.2s -> 5.0s; synthetic 8k-file
mixed repo (K=4000) resolution 16.0s -> 1.7s. Full suite green.

Co-Authored-By: Claude Opus 4.8 (1M context) <noreply@anthropic.com>

* docs: correct stale better-sqlite3/wasm references to node:sqlite

The SQLite backend has been Node's built-in node:sqlite (real SQLite, WAL + FTS5,
from the bundled runtime) for a while — there is no native build step and no
node-sqlite3-wasm fallback. README and the docs site were already updated; this
catches the stragglers:

- CLAUDE.md: the src/db/ backend description and the sqlite-backend test note.
- src/db/index.ts, src/mcp/tools.ts: two code comments that still blamed "the
  wasm backend" for non-WAL behavior (reworded to "when WAL isn't in effect").

Leaves tree-sitter grammar wasm (web-tree-sitter / --liftoff-only) untouched —
that's a different, still-current use of wasm.

Co-Authored-By: Claude Opus 4.8 (1M context) <noreply@anthropic.com>

* chore(telemetry): drop the dead sqlite_backend field (schema v2)

node:sqlite is now the only backend, so the `index` event's `sqlite_backend`
field was a constant ("native") carrying no signal — and the `install` event
never actually sent it. Remove the field and the backendKind() helper, bump the
telemetry SCHEMA_VERSION 1 -> 2, and update TELEMETRY.md + docs/design/telemetry.md.

The ingest worker is deliberately left tolerant: `index` doesn't require the
field and schema_version validates as nonNegInt(99), so v2 events ingest fine and
old clients still sending v1 + sqlite_backend keep validating too. Added a legacy
comment there explaining it's safe to drop once old-client share is negligible.

telemetry.test.ts: the assertion pinning schema_version and a stale-claim fixture
line updated 1 -> 2. All telemetry tests pass.

Co-Authored-By: Claude Opus 4.8 (1M context) <noreply@anthropic.com>

---------

Co-authored-by: Claude Opus 4.8 (1M context) <noreply@anthropic.com>

src/telemetry/index.ts

@@ -30,7 +30,10 @@ import { randomUUID } from 'crypto';
 export const TELEMETRY_ENDPOINT = 'https://telemetry.getcodegraph.com/v1/events';
 export const TELEMETRY_DOCS = 'https://github.com/colbymchenry/codegraph/blob/main/TELEMETRY.md';
 
-const SCHEMA_VERSION = 1;
+// v2: dropped the `sqlite_backend` field from the `index` event — node:sqlite is
+// now the only backend (the better-sqlite3-native / wasm-fallback split is gone),
+// so the value was a constant carrying no signal. See TELEMETRY.md.
+const SCHEMA_VERSION = 2;
 const MAX_BUFFER_BYTES = 256 * 1024;
 const MAX_EVENTS_PER_REQUEST = 100;
 const DEFAULT_FLUSH_TIMEOUT_MS = 1500;
@@ -55,18 +58,13 @@ export function bucketDuration(ms: number): '<10s' | '10-60s' | '1-5m' | '5m+' {
   return '5m+';
 }
 
-/** Collapse a backend identifier (e.g. `node-sqlite`) to the schema's enum. */
-export function backendKind(backend: string): 'native' | 'wasm' {
-  return backend.toLowerCase().includes('wasm') ? 'wasm' : 'native';
-}
-
 /**
  * Shared "a full index completed" event (CLI init/index + installer local
  * init): language names and coarse buckets only — never paths, file names,
  * or exact counts. Structurally typed so callers don't need engine imports.
  */
 export function recordIndexEvent(
-  cg: { getStats(): { filesByLanguage: Record<string, number> }; getBackend(): string },
+  cg: { getStats(): { filesByLanguage: Record<string, number> } },
   result: { filesIndexed: number; durationMs: number },
 ): void {
   try {
@@ -77,7 +75,6 @@ export function recordIndexEvent(
       languages,
       file_count_bucket: bucketFileCount(result.filesIndexed),
       duration_bucket: bucketDuration(result.durationMs),
-      sqlite_backend: backendKind(cg.getBackend()),
     });
   } catch {
     /* telemetry must never break indexing */