[johnybradshaw]

What

scripts/run-tests.mjs now honours an optional GRAFT_TEST_CONCURRENCY=<n> and passes --test-concurrency=<n> to node --test.

• Unset or empty: no change. Node keeps its default of availableParallelism() - 1, so CI and every other contributor behave exactly as before.
• Not a positive integer (0, abc, -2, 1.5): the script exits 1 with ✗ GRAFT_TEST_CONCURRENCY must be a positive integer, got '…' instead of quietly running on every core. The check runs before the run's temp folder is created, so a rejected value leaves nothing behind.

Why

Each test file gets its own Node process, and each one loads tsx. On a shared 8-vCPU dev box running several agent sessions, one npm test held load at ~20 and CPU pressure at ~78% for the whole run, and every other session on the box stalled with it. Contributors need a way to cap that without editing the script.

Verification (Node v24.21.0, Linux)

• GRAFT_TEST_CONCURRENCY=4: sampled the runner's direct children every 2 s; there were exactly 4 test workers throughout (3–4 at the tail), against 7 by default.
• Full suite capped (4) and uncapped: identical results both times, with the same 12 failures in each. Those 12 come from my local environment (grammar/symlink tests against a node_modules borrowed from another checkout) and don't depend on concurrency. CI is green on ae39158, the base of this branch.
• All four invalid values exit 1, and no trail-test-run-* folder is created.

--test-concurrency needs Node ≥ 20.10. The flag is only passed when the variable is set, so engines: >=20 is unaffected.

🤖 Generated with Claude Code

[trailhq-graft]

🌱 graft blast radius

Nothing outside this diff depends on it. 1 area changed; no indexed dependents at depth 2.
Tag: @anirudhkumar-nanonets — Test Runner · @shhdwi — Test Runner

Who knows this code — 2 people across 1 area

Area	Who knows it
Test Runner · changed	@anirudhkumar-nanonets — 2 commits, last 10d ago · @shhdwi — 1 commit, last yesterday

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.

Test signal per changed area — 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.

• – Test Runner — no function, method or class changed here

_{graft blast · origin/main...HEAD · depth 2 · 1 changed file}

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