fix(ida): preserve native workspace admission and startup outcomes

Validate the selected workspace lookup through stat before canonicalization,
preserving typed configuration causes and physical traversal semantics. Cover
readiness without writes and tie startup cleanup regressions to explicit
cancellation or timeout producer outcomes.

Fixes #6828

docs/ida-provider.md

@@ -110,6 +110,13 @@ REA copies the admitted binary into a private temporary directory, checks its di
 
 One REA session owns one database. Stdio registrations default `IDA_MCP_MAX_WORKERS` to `1`; the explicit upstream `--max-workers 1` also bounds a supervisor. Database size and engine memory depend on the target and upstream; REA does not impose an engine memory limit. The original binary is never executed or overwritten. Optional `workspaceRoot` selects an existing absolute temporary-directory parent on the REA host. The selected parent is resolved by the filesystem before deriving its canonical identity, including POSIX symlink/parent components. Ensure it has space for the input copy and IDA working files.
 
+Readiness and allocation check the selected spelling with native
+[`stat`](https://github.com/nodejs/node/blob/v24.22.1/doc/api/fs.md#fspromisesstatpath-options)
+before canonicalizing it. This retains missing and non-directory intermediate
+lookup failures: [macOS `realpath`](https://github.com/apple-oss-distributions/Libc/blob/71bbe350ab79eef58113991d817ccc6165061a64/stdlib/FreeBSD/realpath.c)
+alone can collapse `file/..`. Diagnostics retain the selected spelling; private
+input paths use the canonical parent for upstream identity checks.
+
 When a completed `idb_open` response reports success or is otherwise ambiguous, but no active owned private worker can be verified, REA retains the private workspace even if `idb_list` appears empty. A later close can retry verification if the original owned worker becomes discoverable. A completed explicit `idb_open` rejection retains the existing no-worker cleanup path. This is a local admission/ownership safeguard and **does not** provide a process-termination receipt or change the legacy reaped-worker protocol.
 
 Headless cleanup uses the upstream database lifecycle. Abruptly terminating REA, its proxy, or the supervisor does not establish worker release. Prefer `close_binary` for MCP sessions; after an interrupted process, inspect upstream session inventory and retained workspace diagnostics before removing working files. This adapter does not claim Windows Job Object containment for the upstream detached workers.