Make MCP Search-Result Ids Self-Contained Fetch Handles

Why

A live ChatGPT retest of the 5-tool MCP surface (2026-06-09) showed the search→fetch journey failing on multi-source hosted packages. Search hits carried id = stream:record_id plus a SEPARATE connection_id field, so a model had to carry TWO values between tools. fetch(id) without connection_id returned a typed 409 ambiguous_connection; ChatGPT's rendered envelope buried the second field and its model never completed a fetch (retrying with both fields was verified to work). OpenAI's search/fetch contract treats result ids as single opaque handles; ours leaked a join requirement into the model loop.

What Changes

• Search result ids become self-contained: when a hit carries a connection, the id is {connection_id}/{stream}:{record_id}. The complete handle appears in both model-visible content[] text and structuredContent.results.
• fetch accepts both forms: the self-contained id (no other argument needed — the embedded connection is forwarded to the RS as the canonical connection_id query parameter) and the legacy stream:record_id form with an optional connection_id argument whose semantics are unchanged, including the typed ambiguous_connection 409 path.
• A self-contained id whose embedded connection disagrees with an explicit connection_id argument is rejected with a typed error before any RS call.
• The search content[] preview stops repeating connection_id as a separate field when it is embedded in the id, keeping the prose budget flat.
• Agent-journey regression coverage follows the model-visible-journey canon rule: consume only content[] text, extract the handle, and complete search→fetch on a multi-source fixture without a connection_id argument.

query_records is intentionally out of scope: its results are canonical RS record envelopes whose id values are plain record ids, not composite fetch handles minted for the OpenAI search/fetch contract, so there is no second handle to fold in.

Capabilities

New Capabilities

• None.

Modified Capabilities

• mcp-adapter: search result ids are single opaque fetch handles that encode the source connection; fetch resolves both the self-contained and legacy id grammars.

Impact

• Affected package: packages/mcp-server (src/tools.js, src/server.js instructions, README).
• Hosted MCP inherits the fix through @pdpp/mcp-server/server (handleStreamableHttpRequest); no reference-implementation changes.
• Affected tests: MCP search/fetch integration, token-budget, and new self-contained-id journey suites.
• No REST contract changes, storage changes, or grant-semantics changes.