Merge remote-tracking branch 'origin/master' into cross-family-fs-sandbox

# Conflicts:
#	docs/config-catalog.md
#	docs/cordis-catalog/events.md
#	docs/cordis-catalog/services.md
#	docs/event-producer-consumer.md
#	docs/persistence-catalog.md
#	examples/acp-agent/cordis.yml
#	examples/acp-agent/tests/snapshots/advanced-toolchain/session.1.jsonl
#	examples/acp-agent/tests/snapshots/advanced-toolchain/session.2.jsonl
#	examples/acp-agent/tests/snapshots/advanced-toolchain/session.jsonl
#	examples/acp-agent/tests/snapshots/both-mode-turn/session.jsonl
#	examples/acp-agent/tests/snapshots/permission-switching/session.jsonl
#	examples/acp-agent/tests/snapshots/skill-load/session.jsonl
#	examples/acp-agent/tests/snapshots/text-turn/session.jsonl
#	packages/bash/bash-sandbox/src/index.ts
#	packages/bash/bash/src/types.ts
#	packages/bash/tool-bash/src/index.ts
#	packages/fs/fs/src/index.ts
#	packages/sandbox/sandbox-policy/src/session-mode.ts
#	packages/ui/permission/src/index.ts
#	packages/ui/permission/tests/permission.spec.ts
#	scripts/doc-budgets.manifest.json

packages/fs/fs-sandbox/README.md

@@ -17,3 +17,13 @@ The per-call mode is the tool-stamped effective mode (session override or escala
 The fence is a check in TRUSTED code over a MODEL-CONTROLLED path — the operations are the seam's own (open, rename), only the target path is untrusted, so canonicalize-then-contain is the complete answer to this surface. This mirrors the `code-runtime` stance: containment, not a security boundary. Kernel-grade isolation of untrusted CODE stays `ctx.bash`'s job ([`dsh-bash-sandbox`](../../bash/bash-sandbox/README.md)). The residual TOCTOU (an ancestor symlink swapped between the containment re-check and the syscall) is narrowed by re-canonicalizing immediately before the write and is accepted for this threat model; a kernel-tight boundary needs `openat2`-class primitives not worth their portability cost here.
 
 A denial is a structured `FsError` (`FS_SANDBOX_DENIED`, carrying the effective mode) — no stderr text inference (unlike bash's kernel denials), because an in-process fence knows exactly what it refused. The model-facing `[sandbox: file access denied under <mode> mode]` marker and the one-approved-wider retry live in the tool layer (`dsh-tool-fs`), exactly as bash's do. See [the cross-family fs sandbox RFC](../../../docs/rfc/implemented/feature/2026-07-14-cross-family-fs-sandbox.md).
+
+## Model Experience
+
+Indirectly, through `dsh-tool-fs`, which renders this backend's `FS_SANDBOX_DENIED` refusals as the `[sandbox: file access denied under <mode> mode]` marker plus the same-turn escalation hint.
+
+## Known Limitations and Deferred Work
+
+- **A policy fence, not a kernel boundary** — the check is trusted code over a model-controlled path, so the residual resolve-to-syscall TOCTOU is narrowed (by the in-place re-canonicalization) but not eliminated; adversarial host processes are out of scope. Kernel-grade isolation of untrusted code stays `ctx.bash`'s.
+- **Fence-vs-runner parity is derived, not asserted** — the writable set comes from `writableRoots`, shared with the Seatbelt profile and pinned by a parity test; a runner profile that changed its writable set without that function would drift.
+- **Requires `ctx.sandboxPolicy`** — the backend reads the default mode and workspace root from it and does not confine without it composed.