AST chunking never runs — core.ts ALL_LANGUAGES is an empty stub set

[amondnet]

Summary

src/chunking/core.ts defines ALL_LANGUAGES as an empty stub Set, while the real, populated set already exists in src/indexing/files.ts. Because chunk-source.ts gates AST chunking on isSupportedLanguage() (which reads the empty set), tree‑sitter AST chunking never runs — every file falls back to line chunking.

Evidence

• src/chunking/core.ts:11-14 —

  // Stub for ALL_LANGUAGES until Unit 4 (language detection) lands.
  //   import { ALL_LANGUAGES } from '../indexing/files.ts'
  const ALL_LANGUAGES: ReadonlySet<string> = new Set<string>()

• src/chunking/core.ts:87 — isSupportedLanguage(lang) => ALL_LANGUAGES.has(lang) → always false.
• src/chunking/chunk-source.ts:35-36 — if (language !== null && isSupportedLanguage(language)) { chunkBoundaries = await chunk(...) } → branch never taken.
• src/indexing/files.ts:436 — real export const ALL_LANGUAGES already exists (Unit 4 has landed).
• @kreuzberg/tree-sitter-language-pack (^1.8.1) is installed but effectively bypassed.

Impact

CLAUDE.md specifies "Chunking: tree‑sitter AST‑based with line‑fallback". Currently it is line‑fallback only, so chunk boundaries ignore code structure — directly affecting chunk quality and therefore search relevance.

Acceptance criteria

• core.ts imports ALL_LANGUAGES from ../indexing/files.ts and removes the empty stub set.
• Verify no import cycle is introduced (files.ts ↔ chunking/); restructure if needed.
• Add a test asserting a supported language (e.g. typescript) takes the AST path (isSupportedLanguage('typescript') === true).
• Manual/spot check that AST chunking actually produces structure‑aligned boundaries.

Found during a stub audit.