fix(sep-2663): use renumbered draft error-code constants in tasks scenarios

[panyam]

Fast-follow to the tasks-mrtr extension (#262), addressing post-merge review feedback.

Problem

The tasks extension scenarios hardcoded the JSON-RPC error codes -32003 (Missing Required Client Capability) and -32001 (Header Mismatch). The draft spec types were since renumbered to -32021 and -32020 per modelcontextprotocol#2907 (landed in #353). A server built against the current draft.ts now returns the new codes, so these checks would produce false failures against a conformant server.

#353 updated draft.ts, sep-2575.yaml, and sep-2243.yaml, but #262 had not merged yet, so its tasks files kept the old literals.

Change

• capability.ts, headers.ts, required-task-error.ts now import MISSING_REQUIRED_CLIENT_CAPABILITY and HEADER_MISMATCH from spec-types/draft instead of hardcoding, matching the existing http-standard-headers scenario. The checks assert whatever the schema currently defines, so a future renumber propagates automatically.
• Dropped the now-stale code number from the affected check-ID slugs, e.g. sep-2663-server-returns-32003-when-required becomes sep-2663-server-returns-missing-capability-when-required. This keeps the slug from going stale on any future renumber. Renamed in both the scenario .ts and sep-2663.yaml.
• Updated the sep-2663.yaml requirement text to -32021, consistent with the already-updated sep-2575 and sep-2243 entries.
• Refreshed doc-comments, check descriptions, and error messages to the new codes (interpolating the constant where the string is emitted at runtime).

Notes

• The tasks scenarios remain in pendingClientScenariosList, so default CI is unaffected.
• traceability.json is not touched here. It already predates the upstream renumber (it still shows the old -32001/-32003 in the sep-2575/sep-2243 rows) and is regenerated separately from a full suite run with --results. sep-2663 is not yet represented in the manifest.

Verification

• npm run typecheck clean
• npm run lint clean
• npm test 292 passed

[pkg-pr-new]

Open in StackBlitz

npx https://pkg.pr.new/@modelcontextprotocol/conformance@356

commit: 800ee0d

[panyam]

@pcarleton - Please find the the follow up to 262 here (the upgrades on the error codes based on #353).

The tasks scenarios now import the renumbered constants (MISSING_REQUIRED_CLIENT_CAPABILITY = -32021, HEADER_MISMATCH = -32020) from spec-types/draft instead of the hardcoded -32003/-32001, matching the existing http-standard-headers scenario.

I also renamed the *-32003 check-ID slugs to drop the embedded number (e.g. sep-2663-server-returns-32003-when-required becomes ...-returns-missing-capability-when-required) so they can't go stale on the next renumber.

Ive gone ahead and sanity-checked end to end against my conformant Go SDK server - before the SDK matched the renumber, these scenarios produced 6 failures (tasks/get MUST return -32021; got -32003 across the capability and required-task-error checks, and expected -32020 HeaderMismatch; got -32001 on the header checks). After the fix they are back to green

Published conformance report (SEP-2663 row): https://panyam.github.io/mcpkit/conformance/