Preserve legacy capability report calls

[masnwilliams]

summary

• accept context-only get_more_tools calls from cached clients as a non-recording refresh response
• keep incomplete structured reports out of capability-demand analytics without failing the tool call
• classify genuine input-schema rejections as validation errors

tests

• bun test
• bun x tsc --noEmit
• changed-file Prettier check
• bun run build

---

Note

Low Risk
Behavior is narrowly scoped to exact legacy payloads and analytics labeling; structured reporting and demand capture paths are unchanged.

Overview
Adds backward compatibility for clients still calling get_more_tools with only a context argument after the structured schema rollout. Those calls are intercepted at the tools/call layer (before strict schema validation) and return a successful legacy_schema_refresh_required payload with recorded: false, nudging a tools refresh instead of failing the agent. Partially structured payloads still validate against the full schema and error as before.

get_more_tools is registered via registerTool with the structured Zod input unchanged. Analytics registration order is flipped so instrumentation wraps the legacy shim and still emits tool-call telemetry for compatibility responses. PostHog $mcp_tool_call events for genuine schema rejections on this tool are reclassified from generic Error to validation.

Docs and tests cover the legacy path, partial-input rejection, and validation telemetry.

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Project	Deployment	Actions	Updated
mcp	Ready	Preview	Sep 17, 2026 6:38pm UTC

[rgarcia]

reviewed — the compatibility paths are clear and the targeted tests pass. two things worth addressing:

Questions

• src/lib/mcp/tools/missing-capability.ts:112-119 — the refreshed schema also advertises every structured field as optional. a compliant current client can repeatedly send only context, receive legacy_schema_refresh_required, refresh to the same schema, and never record demand. could we preserve the required fields in the advertised current contract while accepting cached legacy calls at dispatch, or otherwise distinguish refreshed clients?

Test coverage

• src/lib/mcp/analytics.test.ts:346-371 — this test constructs the exact SDK error shape expected by the classifier, so it cannot catch changes in the real instrumentation path. consider sending an invalid get_more_tools call through the existing simulateRequest harness and asserting the captured $mcp_error_type is validation.

[masnwilliams]

addressed both review points in 115f0fd:

• restored all structured fields as required in the advertised schema; the exact legacy context-only payload is handled at dispatch without changing tools/list
• replaced the synthetic classifier test with an invalid call through the instrumented request harness and asserted the captured validation type plus error-text redaction

validated with 606 tests, typecheck, formatting, and a production build.