fix(pty-local): restore the session-resolved workspace policy

The linear replay resurrected the July spawn path: mode folded inline
and both confinement and the default cwd fenced to the deployment
workspaceRoot. Master (and the pre-rebase merge result) resolve the
policy once per spawn — resolve({ session }) — so session.header.cwd
is both the workspace-write boundary and the default shell cwd, as the
README already states. Restores the single resolve, threads the policy
through spawnArgv and the cwd fallback, re-expresses master's
session-root test on the terminal spec, and pins the recorded confine
policy in the explicit-cwd test.

Also from the same review round: the Python SDK exe build stages
pty.node from subprocess-local (node-pty's home since the relocation),
and fs-local's README counts the seam's eleven primitives.

scripts/build-exe-for-python-sdk.ts

@@ -326,7 +326,7 @@ class SingleExeBuild {
     if (this.cli.dryRun) console.log(`build-exe-for-python-sdk: [dry-run] rm -rf ${stagedBuild}`)
     else await rm(stagedBuild, { recursive: true, force: true })
     if (target.platform !== 'linux') return
-    const source = join(root, 'packages', 'pty', 'pty-local', 'node_modules', 'node-pty', 'build', 'Release', 'pty.node')
+    const source = join(root, 'packages', 'subprocess', 'subprocess-local', 'node_modules', 'node-pty', 'build', 'Release', 'pty.node')
     const destination = join(stagedBuild, 'Release', 'pty.node')
     if (this.cli.dryRun) {
       console.log(`build-exe-for-python-sdk: [dry-run] cp ${source} ${destination}`)