fix(ai): McpServer issues with tool strictness, server instructions and prompt titles

[lloydrichards]

Type

• Bug Fix

Description

I'm still in the flow from #7265 so took a look at these recent issues together:

• McpServer: unknown tool-call keys are silently stripped; Tool.StrictJsonSchema is not honoured and there is no way to decode strictly #8218 -> Strict unknown-key rejection. From the MCP tools specification says servers must validate tool inputs against the tool’s advertised inputSchema and since the Tool.Strict is an Effect-specific API contract this needs to Effect.die when an invalid combination is used.
• McpServer: no way to set InitializeResult.instructions #8219 -> Server instructions. String is part of InitializeResult from 2024-11-05 through 2025-11-25 but in 2026-07-28 it was removed and the field moved to DiscoverResult.instructions.
• McpServer.prompt: no way to set the prompt title served in prompts/list #8220 -> Prompt title. Introduced in 2025-06-18 through the prompt’s BaseMetadata.

Related

• Closes McpServer: unknown tool-call keys are silently stripped; Tool.StrictJsonSchema is not honoured and there is no way to decode strictly #8218
• Closes McpServer: no way to set InitializeResult.instructions #8219
• Closes McpServer.prompt: no way to set the prompt title served in prompts/list #8220

Closes EFF-1369

[changeset-bot]

🦋 Changeset detected

Latest commit: 4b4fe25

The changes in this PR will be included in the next version bump.

This PR includes changesets to release 30 packages

Name	Type
effect	Patch
@effect/opentelemetry	Patch
@effect/vitest	Patch
@effect/ai-anthropic	Patch
@effect/ai-openai-compat	Patch
@effect/ai-openai	Patch
@effect/ai-openrouter	Patch
@effect/atom-react	Patch
@effect/atom-solid	Patch
@effect/atom-vue	Patch
@effect/platform-browser	Patch
@effect/platform-bun	Patch
@effect/platform-deno	Patch
@effect/platform-node-shared	Patch
@effect/platform-node	Patch
@effect/sql-clickhouse	Patch
@effect/sql-d1	Patch
@effect/sql-libsql	Patch
@effect/sql-mssql	Patch
@effect/sql-mysql2	Patch
@effect/sql-pg	Patch
@effect/sql-pglite	Patch
@effect/sql-sqlite-bun	Patch
@effect/sql-sqlite-do	Patch
@effect/sql-sqlite-node	Patch
@effect/sql-sqlite-react-native	Patch
@effect/sql-sqlite-wasm	Patch
@effect/docgen	Patch
@effect/doctest	Patch
@effect/openapi-generator	Patch

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[github-actions]

Bundle Size Analysis

Generated from PR build output; treat the content below as untrusted.

File Name	Current Size	Previous Size	Difference
arbitrary-combinators.ts	34.58 KB	34.58 KB	0.00 KB (0.00%)
basic.ts	6.87 KB	6.87 KB	0.00 KB (0.00%)
batching.ts	9.95 KB	9.95 KB	0.00 KB (0.00%)
brand.ts	6.45 KB	6.45 KB	0.00 KB (0.00%)
cache.ts	10.77 KB	10.77 KB	0.00 KB (0.00%)
config.ts	21.51 KB	21.51 KB	0.00 KB (0.00%)
differ.ts	20.32 KB	20.32 KB	0.00 KB (0.00%)
http-client.ts	21.93 KB	21.93 KB	0.00 KB (0.00%)
http-router.ts	33.48 KB	33.48 KB	0.00 KB (0.00%)
logger.ts	10.88 KB	10.88 KB	0.00 KB (0.00%)
metric.ts	9.02 KB	9.02 KB	0.00 KB (0.00%)
optic.ts	6.70 KB	6.70 KB	0.00 KB (0.00%)
pubsub.ts	15.10 KB	15.10 KB	0.00 KB (0.00%)
queue.ts	11.85 KB	11.85 KB	0.00 KB (0.00%)
schedule.ts	10.96 KB	10.96 KB	0.00 KB (0.00%)
schema-binary.ts	39.51 KB	39.51 KB	0.00 KB (0.00%)
schema-class.ts	20.06 KB	20.06 KB	0.00 KB (0.00%)
schema-fromJsonSchemaDocument.ts	30.93 KB	30.93 KB	0.00 KB (0.00%)
schema-representation-roundtrip.ts	26.34 KB	26.34 KB	0.00 KB (0.00%)
schema-string-transformation.ts	13.63 KB	13.63 KB	0.00 KB (0.00%)
schema-string.ts	11.12 KB	11.12 KB	0.00 KB (0.00%)
schema-template-literal.ts	15.41 KB	15.41 KB	0.00 KB (0.00%)
schema-toArbitrary.ts	34.10 KB	34.10 KB	0.00 KB (0.00%)
schema-toCodeDocument.ts	24.56 KB	24.56 KB	0.00 KB (0.00%)
schema-toCodecJson.ts	19.27 KB	19.27 KB	0.00 KB (0.00%)
schema-toEquivalence.ts	19.38 KB	19.38 KB	0.00 KB (0.00%)
schema-toFormatter.ts	19.49 KB	19.49 KB	0.00 KB (0.00%)
schema-toJsonSchemaDocument.ts	23.77 KB	23.77 KB	0.00 KB (0.00%)
schema-toRepresentation.ts	19.54 KB	19.54 KB	0.00 KB (0.00%)
schema.ts	19.27 KB	19.27 KB	0.00 KB (0.00%)
stm.ts	12.80 KB	12.80 KB	0.00 KB (0.00%)
stream.ts	9.83 KB	9.83 KB	0.00 KB (0.00%)

[guillempuche]

You're pushing MCP in Effect, thanks Lloyd!