First-ever build never sets isFullBuild=true, skipping #2032's reachability dead-code downgrade

[carlos-alm]

Summary

codegraph build on a brand-new project (no prior .codegraph/graph.db) always takes the incremental code path internally, never the full-build path — even though there is zero prior state to diff against. This means applyReachabilityDowngrade's whole-graph BFS reachability pass (#2032, PR #2258) never runs on a project's first build; it only runs on a later --no-incremental rebuild. Discovered while validating #2033's end-to-end dead-code scenario.

Root cause

getChangedFiles (src/domain/graph/builder/stages/detect-changes.ts):

let hasTable = false;
try {
  db.prepare('SELECT 1 FROM file_hashes LIMIT 1').get();
  hasTable = true;
} catch (e) { ... }

if (!hasTable) {
  return { changed: allFiles.map((f) => ({ file: f })), removed: [], isFullBuild: true };
}

file_hashes is created via CREATE TABLE IF NOT EXISTS in src/db/migrations.ts, applied unconditionally on every DB open — so hasTable is true even for a freshly-created, zero-row DB. The !hasTable branch (the only place that sets isFullBuild: true in this function) is therefore dead in practice; it only fires for a DB predating the file_hashes migration. A first build instead falls through to mtimeAndHashTiers, which always returns isFullBuild: false (every file appears in tierMtimeSize's needsHash list since existing is an empty Map, and tierHash/mtimeAndHashTiers hard-code isFullBuild: false regardless).

Confirmed via repro:

rm -rf .codegraph && codegraph build   # logs "[codegraph] Incremental: N changed, 0 removed"

ctx.isFullBuild ends up false for the very first build of any project, of any size.

Impact

classifyRoles (src/domain/graph/builder/stages/build-structure.ts) and classifyNodeRoles (src/features/structure.ts) only run the #2032 transitive-unreachable-dead-code downgrade on the full-build path — classifyNodeRolesIncremental deliberately omits it (a partial, changed-files-scoped edge set can't safely answer a whole-graph reachability question). Since a first build is misclassified as incremental, roles --role dead never benefits from #2032's fix until a user explicitly runs codegraph build --no-incremental — a significant, silent gap in the dead-code detector's real-world effectiveness for every fresh clone/first build.

Suggested fix

getChangedFiles should treat an empty file_hashes table the same as a missing one — check SELECT COUNT(*) FROM file_hashes (or reuse the existing row-count probe pattern already used elsewhere, e.g. hasEmptyAnalysisTable in the same file) rather than just table existence, and return isFullBuild: true in that case too.

Related

• roles --role dead: non-transitive fan-in means a function called only by another dead function is never flagged dead #2032 / PR fix(classifiers): detect transitively-unreachable dead code, not just fanIn===0 #2258 — the reachability downgrade this bug silently defeats on first build
• Calls inside object-literal-property closures returned from a factory are misattributed to the enclosing factory, not the property #2033 — where this was discovered while validating the end-to-end dead-code scenario