Support configurable MCP gateway tool timeout via engine.mcp.tool-timeout

[lpcox]

Problem

The MCP gateway has a hardcoded default toolTimeout of 60 seconds. Workflows using slow MCP backends (e.g., Repo Mind Light which requires full-text search over large indexes) hit this timeout even when GH_AW_TOOL_TIMEOUT is set much higher (e.g., 600s).

Root cause: GH_AW_TOOL_TIMEOUT is an env var consumed by the agent container (Copilot CLI), but the MCP gateway — which proxies tool calls between the agent and backend MCP servers — enforces its own independent 60s timeout that is not configurable from the workflow frontmatter.

Evidence: github/pull-requests run 25225648212 shows:

• GH_AW_TOOL_TIMEOUT: 600 (agent env)
• Gateway: toolTimeout=60 (gateway internal default)
• Result: net/http: timeout awaiting response headers on repo-mind query after ~60s

Proposed Solution

Add engine.mcp.tool-timeout to the workflow frontmatter schema, following the same pattern as engine.mcp.session-timeout (PR #29354):

engine:
  mcp:
    tool-timeout: 120   # seconds (or duration string like "2m")
    session-timeout: 6h # already supported

Implementation

1. Schema: Add engine.mcp.tool-timeout property to the JSON schema (integer seconds or duration string)
2. Parsing: Add MCPToolTimeout field to EngineConfig in ExtractEngineConfig
3. Validation: Add validateEngineMCPToolTimeout (bounds: 10s–600s) in engine_validation.go
4. Config propagation: In buildMCPGatewayConfig, propagate to MCPGatewayRuntimeConfig.ToolTimeout
5. Rendering: Pass toolTimeout in the gateway stdin JSON config (requires mcpg support — see companion issue)
6. Default: When not specified, omit from config (gateway uses its own default of 60s)

Frontmatter example

engine:
  mcp:
    tool-timeout: 120

Depends On

• github/gh-aw-mcpg companion issue: mcpg must accept toolTimeout in its stdin JSON config and apply it to HTTP backend requests

Related

• Support configurable MCP gateway session timeout via engine.mcp.session-timeout #29354 — engine.mcp.session-timeout (same pattern)
• github/pull-requests run 25225648212 — Repo Mind Light timeout