feat(dev): add Agent Inspector HTTP layer (server, security, assets)

[tejaskash]

What

First of three stacked PRs re-authoring the Agent Inspector from feat/agent-inspector against current refactor APIs. This one lands the HTTP contract and SPA delivery only — a pure request to response handler the dev command will compose with io/startHttpServer. It is not yet reachable from the CLI.

Stacked on #2041 (feat/dev-supervisor); retarget to refactor once that merges.

Scope

• src/core/dev/inspector/{types,respond,server,testkit}.ts — DI interfaces (InspectorSupervisor, InspectorTraces, InspectorAssets, InspectorDeps), response helpers, and createInspectorHandler.
• src/core/dev/inspectorAssets.ts — reads the staged SPA through AssetSource with an AGENT_INSPECTOR_PATH override and a node_modules fallback.
• src/io/packagedAssets.ts — raw file reads and package-dir resolution, so node:fs/node:module stay out of core/dev.
• scripts/build.ts — stageInspectorAssets() copies @aws/agent-inspector/dist-assets into the asset tree before bundle and compile.

Routes registered this PR: GET /api/status, POST /api/start, GET /api/traces, GET /api/traces/:id, static SPA (with index.html fallback), and a graceful { success:false, error } 404 for everything else. Agent-proxy routes (invocations, MCP, A2A, resources) and the CLI wiring land in the following PRs, so no stub routes appear here.

Security model

Loopback-only Host check (accepts localhost, 127.0.0.1, [::1]), server-side Origin allowlist (plus the Vite :5173 dev origins), X-Agentcore-Local required on POSTs, CORS preflight, and a CSP on served HTML.

Design notes vs the reference branch

• Route matching hardened: exact /api/traces for the list route and slice + decodeURIComponent for :id, so /api/tracesXYZ no longer matches the list route and encoded ids decode. Covered by tests.
• Boundary of concern: filesystem and package resolution moved into src/io/packagedAssets.ts; inspectorAssets.ts no longer imports node:fs/node:module.
• Trace list capped to the newest 200 per poll, matching TraceStore.list's existing limit contract, since each summary carries full spans/logs.
• Security-guard rejection cases parameterized with test.each.

Verification

• bun test src/core/dev/inspector + inspectorAssets.test.ts — 26 pass.
• Full bun test (1812 pass), bun run typecheck, bun run lint:check, bun run format:check all green.
• bun run build stages the four SPA files into src/assets/agent-inspector/ (gitignored) and mirrors them into dist/assets/.

[codecov-commenter]

Codecov Report

❌ Patch coverage is 95.90164% with 10 lines in your changes missing coverage. Please review.
✅ Project coverage is 97.41%. Comparing base (f1a651c) to head (31df625).

Files with missing lines	Patch %	Lines
src/core/dev/inspector/server.ts	96.42%	4 Missing ⚠️
src/core/dev/inspector/testkit.ts	93.75%	3 Missing ⚠️
src/io/packagedAssets.ts	84.61%	2 Missing ⚠️
src/core/dev/inspector/respond.ts	96.87%	1 Missing ⚠️

Additional details and impacted files

@@             Coverage Diff              @@
##           refactor    #2082      +/-   ##
============================================
- Coverage     97.42%   97.41%   -0.02%     
============================================
  Files           429      434       +5     
  Lines         26314    26558     +244     
============================================
+ Hits          25637    25871     +234     
- Misses          677      687      +10     

☔ View full report in Codecov by Harness.
📢 Have feedback on the report? Share it here.

🚀 New features to boost your workflow:

• ❄️ Test Analytics: Detect flaky tests, report on failures, and find test suite problems.
• 📦 JS Bundle Analysis: Save yourself from yourself by tracking and limiting bundle sizes in JS merges.

[agentcore-devx-automation]

Claude Security Review: no high-confidence findings. (run)

[AlexanderRichey]

Is this helper necessary? Looking at where it's used, it doesn't seem to be reducing complexity or cognitive load? In other words, the code above would be just as easy to follow, or even easier, without this little helper.

[AlexanderRichey]

Primarily copy/pasting stuff as is, right?

[tejaskash]

Primarily copy/pasting stuff as is, right?

Yep, split up into smaller chunks to make it easier to read

[agentcore-devx-automation]

Claude Security Review: no high-confidence findings. (run)