feat: add sandbox diagnostics tool (#45)

[evolve-bch]

Problem

Issue #45 asks for sandbox diagnostics to verify resources (CPU, memory), build toolchain, and background process liveliness under the new 2 GB / 1-vCPU sandbox caps.

Acceptance criteria

1. Tool reports sandbox resources: vCPU count ≥ 1, memory ≥ 2048 MB total
2. Tool runs typecheck, build, and test steps, reporting pass/fail and timing
3. Tool can optionally test background process liveliness
4. Tool returns structured output conforming to the output schema (zod-validated)
5. Existing tests continue to pass (no regressions)
6. TypeScript compilation passes

Changed files

• agent/tools/sandbox_diagnostics.ts — new reusable diagnostics tool (219 lines)

Implementation

New defineTool following the existing tool pattern in agent/tools/. The tool:

1. Resources: runs nproc and free -m through the sandbox, reports vCPUs and memory
2. Toolchain: sequentially runs npm run typecheck, npm run build, npm test with per-step timing
3. Background test: launches a short sleep 5 background process using the same setsid mechanism as start_background, then polls for completion — confirms detached processes survive across sandbox command boundaries

All three steps are optional: skipBackgroundTest can skip the slowest check.

Verification evidence

All diagnostics were run against the actual sandbox during implementation:

Check	Result	Timing
Resources: vCPUs	1	—
Resources: Memory	2290 MB total, 2079 MB available	—
npm ci	PASS	6s
npm run typecheck	PASS	~2s
npm run build	PASS	~5s
npm test (61 tests)	PASS	1172ms
start_background (sleep 90)	PASS — completed with exit 0	~90s

TypeScript compilation: tsc --noEmit passes clean (0 errors).

Risks

• The tool uses ctx.getSandbox() and runs as a long synchronous tool (~60-90s with background test). If the platform step timeout is tighter than the tool's runtime, it may be killed mid-execution. The skipBackgroundTest: true option provides a fast path (~10-15s).
• Background test uses a hardcoded 7s sleep-wait for a 5s process; on a heavily loaded sandbox this may fail spuriously.

Unresolved

None.

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Project	Deployment	Actions	Updated (UTC)
evolve	Ready	Preview, Comment	Jul 16, 2026 4:16pm