training-agent: re-add identity.brand_json_url emit after 3.1 SDK pin bump

[bokelley]

Background

#3690 added identity.brand_json_url to get_adcp_capabilities and wired the training agent to emit it (plus identity.key_origins.request_signing when signing is supported). The emit was reverted in the same PR (commit 89c38e74c) because the storyboard runner uses @adcp/sdk's pinned ADCP_VERSION='3.0.1' to fetch the response schema from adcontextprotocol.org/schemas/3.0.1/..., and that published schema doesn't have the new field.

The right fix is a coordinated SDK version bump after 3.1 ships. This issue tracks re-adding the emit then.

What's already in place

• AdCP-domain /.well-known/brand.json (server/src/http.ts:634) lists the training agent in agents[] with the JWKS URI — eTLD+1 origin binding passes without authorized_operators[].
• E2E script scripts/e2e-resolve-training-agent.ts exercises the full chain in --inproc mode against fixtures.
• A deferral comment in server/src/training-agent/framework-server.ts marks where the emit is meant to go back.

Re-add when

1. AdCP 3.1 published (currently 219 changesets queued, no published timeline).
2. @adcp/sdk bumps ADCP_VERSION to a 3.1.x release that includes identity.brand_json_url in the published schema bundle.

Implementation

Re-add the overrides.identity block in framework-server.ts and the inline identity block in task-handlers.ts handleGetAdcpCapabilities. Both were deferred in the same commit (89c38e74c2); the diff to revert is small and self-contained. Verify the storyboard runner accepts the new field by re-running framework + legacy storyboards on a PR.

After re-add, the e2e script's HTTP mode (npx tsx scripts/e2e-resolve-training-agent.ts http://localhost:3000) should resolve the chain end-to-end against the live training agent — currently only --inproc works because the production agent doesn't emit the field.

Related

• Schema land: #3690 (merged, 3.1)
• SDK ports waiting on the same SDK pin bump: adcp-client#1268, adcp-client-python#344, adcp-go#109

Acceptance

• @adcp/sdk bumped to a 3.1.x version that includes identity.brand_json_url in its bundled schemas
• framework-server.ts overrides.identity block restored
• task-handlers.ts handleGetAdcpCapabilities identity block restored
• Storyboard runner accepts the new field (framework + legacy dispatch)
• E2E script HTTP mode resolves against the live training agent

[bokelley]

/triage

[bokelley]

Manual triage (routine HTTP 429)

Classification: bug (deferred follow-up)
Labels/Milestone: bug, addie — Evergreen
Status: blocked-on AdCP 3.1 publish + @adcp/sdk ADCP_VERSION bump to 3.1.x

Re-add the identity.brand_json_url + identity.key_origins.request_signing emits in training-agent/framework-server.ts after 3.1 ships and the SDK pin lands.

Verification checklist when unblocked:

1. @adcp/sdk ships a release pinning ADCP_VERSION to 3.1.x
2. The 3.1.x get-adcp-capabilities-response.json schema in dist/schemas/3.1.x/ includes the identity.brand_json_url field
3. Storyboard runner picks up the new schema (no Zod-strict bypass needed)
4. Re-add the emit at the location flagged in the deferral comment
5. scripts/e2e-resolve-training-agent.ts passes end-to-end

Watching: 3.1 release queue (219 changesets queued per the issue body).