call-actor mixes Apify-run and MCP-tool pass-through under one schema

[MQ37]

Problem

call-actor does two unrelated things under one tool name:

Input shape	Path	Returns
actor: "apify/rag-web-browser"	Apify run via SDK	Canonical RunResponse (waitSecs, storages, summary, nextStep)
actor: "apify/actors-mcp-server:fetch-apify-docs"	Pass-through to remote MCP tool	Arbitrary remote content + isError

#859 patches the immediate SDK-rejection bug by synthesizing a sentinel RunResponse, but runId: 'mcp-passthrough' / actorId: <serverName> / empty storages are dishonest values for a path that has no run. The schema fits, the semantics don't.

// src/tools/core/call_actor_common.ts (after #859)
return {
    content: result.content,
    isError: isErrorFromRemote,
    structuredContent: {
        runId: 'mcp-passthrough',          // ← sentinel, no Apify run exists
        actorId: baseActorName,             // ← actor ID, not "actor that produced this content"
        actorName: baseActorName,
        status: isErrorFromRemote ? 'FAILED' : 'SUCCEEDED',
        storages: {},                       // ← always empty
        summary: `Called MCP tool '${mcpToolName}' on '${baseActorName}'.`,
        nextStep: 'Response content carries the remote MCP tool result; no Apify run was started.',
    },
};

LLMs reading tools/list see one call-actor with one outputSchema, but the actual return shape depends on whether the actor string contains a :. Side effects: waitSecs is silently ignored on pass-through, taskMode reaches the path but is meaningless, telemetry mixes run starts with MCP tool calls.

Fix

Pick one direction:

Option A — separate tool: keep call-actor for Apify runs only; add call-mcp-actor-tool (or similar) with its own input schema (actor, tool, input), its own output schema mirroring the remote MCP CallToolResult shape, and no waitSecs / taskMode. Tool descriptions disambiguate, both can be auto-injected when an MCP-server Actor is in scope.

Option B — code mode as the default: position code mode (where the model writes JS/Python that calls apifyClient directly) as the recommended path for MCP-server Actor tools, deprecate the pass-through syntax over one minor cycle, remove it.

Out of scope

• The immediate SDK -32600 error — covered by fix(call-actor): synthesize structuredContent on MCP server pass-through #859.
• The pre-actor:"X:Y" "MCP server but no :tool" guard — already handled by CALL_ACTOR_MCP_MISSING_TOOL_NAME_MSG.

[MQ37]

FYI @jirispilka