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mcpx: Phase 3 of #1481 — validate elicitation form answers against requestedSchema in client.answer #1484
Description
Phase 3 of design #1481 (JSON Schema validation of tool input and output). Design doc: files/designs/code-mcpx-json-schema-validation.md in the keep-the-four-repos-healthy goal workspace. Origin gap: dezren39/darwin-nix#254 (acceptance: "Elicitation schemas are validated with the same mechanism").
Dependency gate: do not start until Phase 1 (the internal/schemaval core) is merged. Independent of Phase 2 — either order after Phase 1 is fine. If claimed earlier, park naming the dependency.
Scope
Validate elicitation form answers against the schema the server itself supplied, at the single answer choke point:
- In
Client.answer(internal/mcpclient/modern.go:253, theelicitation/createcase), afterapplyDefaultsruns (defaults first — an omitted field is valid only once its default is in): when the mode is form (or undeclared, which the codebase already treats as form) and the handler's answer hasaction: "accept"withcontent, compile the request'srequestedSchemawithschemavaland validatecontentagainst it. - On failure: return an Invalid Params (-32602)
rpcErrorto the requesting server naming the failing path, emit aWarning, and do not relay the answer. The unvalidated answer never reaches the upstream. - On a
requestedSchemathat itself does not compile: warn and relay the answer unvalidated (the server authored the schema; its defect must not wedge the user's answer) — record this choice in a code comment. - Untouched:
decline/cancelanswers (no content to validate), URL mode, sampling (sampling/createMessage— gap fix(id): show world chat only to participants who may chat or read history #256, separate), and the broker/daemon layers (the modern input-required flow inherits this check becauseresolveInputroutes throughanswer()). - Update the conformance matrix / gap registry for the elicitation validation rows this closes (
elicitation-both-validate-against-schema,elicitation-client-validate-responses,elicitation-server-validate-received-data— the mechanism rows shared with fix(id): coalesce LogSync ingest batches (#241) #255).
Out of scope: everything else under #255 (elicitation storage protection, redaction, CLI review UI); re-ask/retry UX for a rejected answer (open question territory — v1 surfaces the -32602 to the server, matching how the undeclared-mode check already behaves in the same function).
Acceptance
- Defining test: a handler answers
acceptwith a wrong-typed field againstrequestedSchema→ the upstream receives -32602, not the answer; aWarningwas emitted. - Defining test: an answer omitting a field that
requestedSchemagives adefaultvalidates and is relayed with the default applied (defaults-before-validation order proven). - Defining test: a conforming answer is relayed byte-identical to today's behaviour; decline and cancel answers pass through with no validation attempted.
- Defining test: an uncompilable
requestedSchema→ answer relayed, warning emitted, no error to the server. - The same wrong-typed answer arriving via a modern input-required round is likewise rejected (the
answer()inheritance is covered by a test, not just asserted). - Full suite passes:
cd pkgs/mcpx && go test ./...(via CI on the PR per fleet policy).
agent-note:v1 — filed by the repo design architect (dedicated code job, pass 3, 2026-10-27) as a sub-issue of design #1481. Filed as task/triage: triage confirms scope against current main once Phase 1 has landed (gate above) and enqueues the implementation packet; do not implement in the triage task.
Activity
developing-today commentedon Oct 27, 2026
CODE-555
dezren39 commentedon Oct 27, 2026
Intake review
🤖 Agent note · filed
Related: #1481 (parent design, decision recorded there), #1482 / #1483 / #1484 (the three phases), dezren39/darwin-nix#254 (origin).
Liveness: searched merged PRs for
schemaval/ schema-validation work — none merged. Not solved; the Phase 1 dependency gate in the body still governs start order.Notes / risks: the body's
## Acceptancesection is a full acceptance-criteria set in substance (defining tests enumerated), so no duplicate criteria section was appended;status/needs-triageadded to complete the filed-state label set. This item already carries queue/queued — triage via the queue, do not implement in the triage task (per the filer's note).Suggested approach: exactly as scoped in the body; park on claim if the Phase 1 gate has not cleared, naming the dependency.
dezren39 commentedon Oct 28, 2026
🤖 Agent note · picked up
Client.answer, state the Phase 1 (mcpx: Phase 1 of #1481 — schemaval core: a real JSON Schema 2020-12 validator + dialect policy (no call-path changes) #1482) dependency, and route the implementation follow-up. No implementation in this task.19 remaining items
dezren39 commentedon Oct 28, 2026
Parked again — dependency gate still unmet (re-checked fresh this shift).
pkgs/mcpx/internal/schemavalis absent from main (contents API 404, checked 2026-10-28T04:31Z; internal/ listing has no schemaval entry).dezren39 commentedon Oct 28, 2026
Gate update (Lane B, task 1616 shift): Phase 1 #1482 has MERGED (PR #1570, main 1da6d84, 2026-10-28T04:51Z) and
pkgs/mcpx/internal/schemavalis on main. The dependency gate on this Phase 3 task (1619) is now satisfied — it resumes on its park schedule and can implement against schemaval. Phase 2 (#1483) is implemented in PR #1596 as the sibling reference for the CallTool wiring.dezren39 commentedon Oct 28, 2026
Picked up by Lane B queue worker (queue task 1619) — dependency gate re-checked fresh and now SATISFIED: #1482 is CLOSED (merged via PR #1570) and
pkgs/mcpx/internal/schemavalexists on main. Proceeding to implement elicitation answer validation inClient.answerper the packet. Labels updated to queue/claimed + status/in-progress.dezren39 commentedon Oct 28, 2026
Done (queue task 1619): dependency gate lifted (#1482 merged via PR #1570, schemaval on main) and Phase 3 implemented — PR #1606:
Client.answernow validates accepted form answers againstrequestedSchemaviainternal/schemavalafterapplyDefaults(-32602 naming the failing path + Warning on failure, answer not relayed; uncompilable schema → warn and relay unvalidated; decline/cancel and URL mode untouched; input-required rounds inherit viaanswer()). New defining tests pass on the laptop; conformance gaps for the three elicitation validation rows retired with covers and the matrix regenerated. Full suite runs via CI on the PR (pending). Task completed as pr_opened.Merge pull request #1606 from developing-today/queue/1619-1484-elicit…
dezren39 commentedon Nov 3, 2026
agent-note:v1
Transition: triage closure (via parent task 2592)
Worker: repo-worker-code (lane code-e)
Closing as completed: Phase 3 was implemented by task 1619 in PR #1606, MERGED 2026-10-30T05:16Z. Verified fresh 2026-11-03: current main carries pkgs/mcpx/internal/mcpclient/elicitation_schema.go wiring internal/schemaval into elicitation answers (Phase 3), its defining tests in elicitation_schema_test.go, and the conformance-matrix update in PR #1606's file list. The issue stayed open only because task 1619 completed as pr_opened; no work remains on this phase.