fix(mcp): cap ui-apps build concurrency to avoid oom#60156
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MCP UI Apps size report
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Size Change: 0 B Total Size: 80.1 MB ℹ️ View Unchanged
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skoob13
approved these changes
May 27, 2026
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Problem
The MCP container image build OOM-kills Vite (exit 137, e.g.
generated/session-summary) at thebuild:ui-appsstep.build-ui-apps.tsdefaulted concurrency toapps.lengthand only capped it to 4 whenprocess.env.CIwas set — but DockerRUNlayers don't inherit the runner'sCIenv, so inside the image build all 28 apps spawned at once and saturated the builder (~98% peak memory in Depot telemetry).Changes
Cap the default to
Math.min(apps.length, 4)and drop theCIgating. The constraint is memory, not which environment we run in, so the default should be safe everywhere — CI, the Docker build, and local dev — with no Dockerfile or Depot changes.How did you test this code?
Agent-authored (Claude Code), automated only — no manual UI testing. Ran the full
build:ui-appsat concurrency 4 (the path this fix selects) end-to-end: all 28 apps built successfully, includinggenerated/session-summary. Confirmed via Depot build telemetry that the failing builds peaked at 97–98% memory and OOM-killed a Vite process.Publish to changelog?
no
Docs update
No docs change needed.
🤖 Agent context
Authored with Claude Code (Bash, Edit, Depot telemetry probing via session cookie).
Diagnosed from the failing Depot builds: 28 Vite processes ran concurrently because the existing 4-worker limiter was gated on
CI, which BuildKitRUNsteps never see. Considered and rejected the env-based fixes —ENV CI=truein the Dockerfile (overloads a semantic flag, bakes build intent into an image layer) and a--max-old-space-size=512heap cap (a singlesession-summarybuild already peaks at ~650 MB RSS, so the cap has no headroom and would turn an intermittent infra OOM into a deterministic per-app crash). Chose to fix the actual defect: the unbounded default. Requires human review.