* fix(mcp): avoid cache resets for unrelated config changes
extensions_config.json carries MCP servers, skills and middleware settings, but the MCP cache treated any whole-file signature change as MCP state change, so toggling a skill retired every cached tool and closed all pooled sessions.
Record a snapshot of the effective MCP slice (enabled servers' parsed config plus mcpInterceptors) and retire MCP state only when that slice changes. Hand the exact config revision to tool discovery so a change during discovery cannot publish tools built from a superseded revision, and add a non-initializing refresh entry point so disabling the last enabled server still converges the cache and pool on the next tool assembly.
* docs(mcp): align cache guide and restore error diagnostics
Review feedback on #5750 flagged three non-blocking issues: the MCP module guide still described the pre-semantic-snapshot invalidation contract; the tools.py sanitization covered every exception in the MCP block, discarding diagnostics for failures that cannot carry resolved credentials; and _is_cache_stale()'s docstring presented it as a pure predicate despite adopting a new file signature.
Narrow the type-only logging to ExtensionsConfig.from_file() and restore logger.exception() for tool caching, pool cleanup and plugin filtering, with a regression test asserting the message and traceback survive. Document the effective-MCP-slice comparison, the stable config handoff to discovery, refresh_mcp_cache_if_active() and the _initialized_without_config handling in the module guide, and note the signature-adoption side effect in the docstring.
* fix(mcp): unify config normalization and verify signatures
Review follow-up on #5750.
- Normalize mcpInterceptors (bare string == single-element list; missing key == empty list) and the type/transport alias through one shared module used by the tools cache, the interceptor builder and the durable-task config snapshot, so equivalent spellings no longer retire tools/sessions or raise McpTaskConfigurationError.
- Treat a resolved-path switch as a signal to re-read the effective MCP slice instead of an invalidation reason: an identical slice adopts the new path and signature and keeps pooled sessions.
- Refuse to publish or adopt a signature whose sha256 digest is missing ((mtime, size, None) from a file that could not be read).
- Sync the English and Chinese MCP user docs with the effective-config comparison, and document that the Gateway admin reset stays unconditional.
* docs(mcp): note the unverifiable-signature fail-closed branch
A present config file whose content cannot be hashed is treated as stale, unlike a deleted file which keeps the last-known-good cache. Record that asymmetry in the module guide.
* docs(mcp): scope the no-hash rationale to never-initialized processes
The cost-free early return in refresh_mcp_cache_if_active() only covers a process that never published an MCP cache. A process that did publish one (including an empty cache from the zero-server or LangGraph Studio lazy-init path) still pays one stat+sha256 per tool assembly. Correct the rationale in the docstring and the matching comment in get_available_tools().
