⚡️ parallelize --deep synthesis batches

[mezis]

Why

--deep concept synthesis still runs one LLM batch at a time. File summaries already honour -j; this pass does not, and engine.init() never received --concurrency.

On a large repo (~6k files, 98 synthesis batches) that serial wait is many hours. Each batch is a long call (~48k chars in, 8k tokens out). A local or OpenAI-compatible server can overlap them; today the GPU/API sits idle between batches.

The change

• Thread -j / --concurrency into graft init (and workspace child builds).
• Run synthesis through the same mapWithConcurrency pool as summaries.
• Per-batch catch + LlmFailureGate: a dead provider stops further calls; a throw does not drop in-flight siblings; empty results stay uncached (--allow-partial still sees result.errors).
• Progress: start and result are each a full stderr line, so concurrent batches do not share a \r spinner.

Tests

• node --import tsx --test test/context.test.ts — overlap under -j 2; a throwing batch keeps siblings
• existing synth/crux read results only from toolCalls; gateways that ignore forced tool_choice silently produce empty/degraded graphs #129 empty-batch / zero-link logs still match

[trailhq-graft]

🌱 graft blast radius

3 areas changed → 1 area can be affected. 1 dependent symbol, depth 2.
Tests: no test reaches Workspace Child Building; CLI Initialization has tests the diff did not touch; 1 area updated its tests.
Tag: @anirudhkumar-nanonets — 3 of 4 areas · @shhdwi — 3 of 4 areas · @Frankie-Xu — Build Context

flowchart TB
  A0(("Workspace Splitting<br/>1 symbol"))
  classDef reached fill:#D9EDF3,stroke:#3AA7C9,stroke-width:1.5px,color:#0E313C;
  class A0 reached;

Loading

Can be affected	Symbols	Nearest hop	Reached from
Workspace Splitting	1	src/graph/workspace.ts:L709-L722 splitWorkspace — calls, depth 1	CLI Initialization, Workspace Child Building

Who knows this code — 4 people across 4 areas

Area	Who knows it
CLI Initialization · changed	@anirudhkumar-nanonets — 42 commits, last today · @shhdwi — 24 commits, last 1mo ago
Workspace Child Building · changed	@shhdwi — 3 commits, last 1mo ago · @anirudhkumar-nanonets — 2 commits, last 1mo ago
Build Context · changed	@anirudhkumar-nanonets — 4 commits, last 27d ago · @Frankie-Xu — 2 commits, last 16d ago
Workspace Splitting · affected	@shhdwi — 6 commits, last 1mo ago · Buseong Kim — 2 commits, last 16d ago

Ownership is git history over each area's own files, weighted towards recent work (120-day half-life). Merge commits and bots are dropped, and you are dropped from your own PR. A name with no @ has no GitHub handle in its commit email — tag them by hand, or add a .mailmap entry. A suggestion from history, not a CODEOWNERS rule.

All 1 dependent symbol, grouped by area

Workspace Splitting — 1 symbol in 1 file

• src/graph/workspace.ts:L709-L722 — splitWorkspace (calls, depth 1)
  712: buildChild: (childDir: string, childName: string) => Promise<void>,

Test signal per changed area — 1 ✓ · 1 ⚠ · 1 ✗

Reached = a node under a test path has a resolved edge into the changed symbol. It undercounts anything called indirectly — through a CLI, a spawned process or a dynamic import — so read a low ratio as “look here”, never as a coverage gate.

• ⚠ CLI Initialization — 1 of 1 reached · 1 test file reaches it, none changed here
• ✗ Workspace Child Building — 0 of 1 reached · no test file reaches it
  • not reached: buildChild
• ✓ Build Context — 1 of 1 reached · 1 test file changed here: test/context.test.ts

5 test suites also reference this code

5 symbols, kept out of the diagram and the table so they cannot crowd out the areas a reviewer has to look at.

• test/context-checkpoint.test.ts
• test/context-only-dir.test.ts
• test/covers.test.ts
• test/utf16-source.test.ts
• test/workspace.test.ts

_{graft blast · origin/main...HEAD · depth 2 · 5 changed files}

Open the interactive graph → — click an area to see its dependent symbols at file:line.