fix(a2a): serve agent card endpoint-relative + every spelling Copilot probes - #243
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…ilot probes Copilot Studio auto-discovers the agent card at browser time by trying a spread of paths and falling back to the origin root — so registration succeeds off our root `/.well-known/agent-card.json`. But its RUNTIME orchestrator resolves the card RELATIVE TO THE REGISTERED ENDPOINT (`https://…/a2a`), i.e. `GET /a2a/.well-known/agent-card.json`, which we did not serve. That 404 fails Microsoft-side with a bare "SystemError" before any request reaches us — confirmed 2026-08-30: zero POST /a2a during the failing window, only 404s on the endpoint-relative card path. Serve the card at every filename Copilot was observed probing (agent-card.json, agent.json, agentcard.json, agentCard.json, agent_card.json) at BOTH the origin root and under `/a2a/.well-known/`. Removes the registration friction (8 of 10 discovery probes were 404ing) and is the likely fix for the runtime SystemError. Verified: the card discovery test now asserts all 10 paths 200. Co-Authored-By: Claude Fable 5 <noreply@anthropic.com>
Co-Authored-By: Claude Fable 5 <noreply@anthropic.com>
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Why
Copilot Studio registration mechanically succeeds but the first real turn returns a bare
SystemError— and nothing reaches our/a2aendpoint (confirmed 2026-08-30 in lab ingress logs: zeroPOST /a2aduring the failing window).Root cause: Copilot's browser-time discovery probes a spread of card paths and falls back to the origin root, so it finds our
/.well-known/agent-card.json(200) and registration completes. But its runtime orchestrator resolves the card relative to the registered endpoint (https://agent-lab.data-zoo.de/a2a) →GET /a2a/.well-known/agent-card.json→ 404 →SystemError, before it ever POSTs.The same logs show Copilot probing 5 filename spellings (
agent-card.json,agent.json,agentcard.json,agentCard.json,agent_card.json) at both root and/a2a/.well-known/— 8 of 10 were 404ing.What
Serve the card at all five spellings at both the origin root (browser discovery) and under
/a2a/.well-known/(runtime, endpoint-relative). Costs nothing; removes every discovery guess and is the likely fix for the runtime SystemError.a2a_spec.rs:CARD_FILENAMESconst + loop; newcard_router_nestedfor the/a2amount.triton-embed: merge the nested card router into the/a2anest.the_agent_card_is_public_and_describes_the_endpointnow asserts all 10 paths return 200.Verification
cargo test -p triton-tests --test it a2a→ 21 passed; clippy clean. Live E2E against lab follows the agent-template vendor bump.🤖 Generated with Claude Code
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