docs(agents): cover HTTP response middleware

Signed-off-by: Piotr Mlocek <pmlocek@nvidia.com>

Author: pimlock

.agents/skills/debug-openshell-cluster/SKILL.md

@@ -109,9 +109,9 @@ journalctl -u openshell-gateway --no-pager --lines=200
 openshell logs <sandbox-name> --tail --source sandbox
 ```
 
-The middleware service must start before the gateway and be reachable from both the gateway and sandbox supervisors. Gateway startup fails if `Describe` is unavailable, a manifest exposes duplicate operation/phase bindings, the registration claims the reserved `openshell/` namespace, or payload and timeout limits are invalid. Supported V1 bindings are `HTTP_REQUEST/PRE_CREDENTIALS` and `WEBSOCKET_MESSAGE/PRE_CREDENTIALS`. When gateway JWT signing is disabled, supervisors preserve the legacy unauthenticated connector and do not request extension credentials. When signing is enabled, credential acquisition and verification failures are fail closed: check HTTPS trust and hostname validation, audience and issuer agreement, the token `kid`, gateway `RefreshSandboxToken` errors, and middleware logs. Changing a registration requires a gateway restart. A policy update can also fail before persistence if the selected implementation rejects its `network_middlewares` config.
+The middleware service must start before the gateway and be reachable from both the gateway and sandbox supervisors. Gateway startup fails if `Describe` is unavailable, a manifest exposes duplicate operation/phase bindings, the registration claims the reserved `openshell/` namespace, or payload and timeout limits are invalid. Supported V1 bindings are `HTTP_REQUEST/PRE_CREDENTIALS`, `HTTP_RESPONSE/PRE_RETURN`, and `WEBSOCKET_MESSAGE/PRE_CREDENTIALS`. When gateway JWT signing is disabled, supervisors preserve the legacy unauthenticated connector and do not request extension credentials. When signing is enabled, credential acquisition and verification failures are fail closed: check HTTPS trust and hostname validation, audience and issuer agreement, the token `kid`, gateway `RefreshSandboxToken` errors, and middleware logs. Changing a registration requires a gateway restart. A policy update can also fail before persistence if the selected implementation rejects its `network_middlewares` config.
 
-At request time, distinguish attachment, binding selection, coverage, denial, and failure. A host-matched HTTP-only attachment can inspect the upgrade GET but does not join the WebSocket chain; the connection proceeds under either `on_error` mode and emits `binding_not_selected` coverage. A selected WebSocket stage receives text messages only. Binary messages pass under both modes, emit `unsupported_message_type` coverage, and consume a session sequence without an RPC. An explicit `middleware_denied` result is always enforced. WebSocket preflight returns `INSPECT`, voluntary `SKIP`, or authoritative `DENY`; `DENY` rejects the upgrade before upstream contact under both `on_error` modes. A selected-stage failure follows the policy-local `on_error`: `fail_closed` blocks the HTTP request or closes the WebSocket, while `fail_open` bypasses only that stage and emits a detection finding. A fail-open per-message capacity failure bypasses that message without disabling the stage. A timeout, transport failure, stream closure, missing or invalid response, duplicate or regressed sequence, or other failure that makes an established WebSocket stream unreliable disables that stage for later messages on the connection and emits `openshell.middleware.websocket_stage_disabled`. Confirm preflight, session-start, and session-end in service logs. OpenShell best-effort sends at most one session-end to each still-writable opened stage, including a preflight that terminates before session start; distinguish `MIDDLEWARE_DENIAL` from `MIDDLEWARE_FAILURE`. WebSocket message sequences are allocated session-wide; each stage receives a strictly increasing subset, so gaps are valid when binary messages or other units are not delivered to that stage. Zero, duplicate, or regressed sequences are protocol errors. If a running supervisor cannot install a new registry, it preserves its last-known-good generation and emits a configuration failure event.
+At request time, distinguish attachment, binding selection, coverage, denial, and failure. Response middleware selects `HEADERS_ONLY`, `WHOLE_BODY_BYTES`, or `STREAM_BYTES` during `HTTP_RESPONSE/PRE_RETURN` preflight. A fail-closed response failure returns canonical `502 response_delivery_failed` before commitment and aborts delivery after commitment; fail-open disables that stage, continues with retained input, and emits both HTTP activity and a sanitized detection finding. A host-matched HTTP-only attachment can inspect the upgrade GET but does not join the WebSocket chain; the connection proceeds under either `on_error` mode and emits `binding_not_selected` coverage. A selected WebSocket stage receives text messages only. Binary messages pass under both modes, emit `unsupported_message_type` coverage, and consume a session sequence without an RPC. An explicit `middleware_denied` result is always enforced. WebSocket preflight returns `INSPECT`, voluntary `SKIP`, or authoritative `DENY`; `DENY` rejects the upgrade before upstream contact under both `on_error` modes. A selected-stage failure follows the policy-local `on_error`: `fail_closed` blocks the HTTP request or closes the WebSocket, while `fail_open` bypasses only that stage and emits a detection finding. A fail-open per-message capacity failure bypasses that message without disabling the stage. A timeout, transport failure, stream closure, missing or invalid response, duplicate or regressed sequence, or other failure that makes an established WebSocket stream unreliable disables that stage for later messages on the connection and emits `openshell.middleware.websocket_stage_disabled`. Confirm preflight, session-start, and session-end in service logs. OpenShell best-effort sends at most one session-end to each still-writable opened stage, including a preflight that terminates before session start; distinguish `MIDDLEWARE_DENIAL` from `MIDDLEWARE_FAILURE`. WebSocket message sequences are allocated session-wide; each stage receives a strictly increasing subset, so gaps are valid when binary messages or other units are not delivered to that stage. Zero, duplicate, or regressed sequences are protocol errors. If a running supervisor cannot install a new registry, it preserves its last-known-good generation and emits a configuration failure event.
 
 For network policy validation failures, first distinguish a gateway mutation
 rejection from a supervisor runtime rejection. Direct policy updates,
@@ -622,6 +622,7 @@ openshell logs <sandbox-name>
 | Policy mutation returns `FAILED_PRECONDITION` for endpoint ambiguity | Equally specific effective endpoint selectors disagree on connection or request-processing metadata | CLI error, base and provider-composed policy, affected profile attachments; confirm no new revision was stored |
 | Supervisor enters policy quarantine | A runtime candidate failed validation while `policy_validation_failure_mode = "fail_closed"` | Sandbox OCSF config/finding events, validation rationale, active generation, `previous_policy_active` |
 | HTTP request returns `middleware_failed` or `middleware_denied`, or WebSocket closes with `1008` | Selected stage failed or explicitly denied admitted traffic | Sandbox OCSF logs; policy-local middleware config; service availability; binding operation; `on_error` |
+| HTTP response returns `response_delivery_failed` or ends after partial delivery | A fail-closed `HTTP_RESPONSE/PRE_RETURN` stage failed before or after response commitment | Sandbox HTTP activity and detection findings; middleware failure category; response framing; service timeout, capacity, and transport logs. Retrying may repeat upstream side effects |
 | WebSocket upgrades but a host-matched middleware receives no preflight or message RPC | The implementation did not advertise `WEBSOCKET_MESSAGE/PRE_CREDENTIALS` | `WEBSOCKET_MIDDLEWARE_COVERAGE state=binding_not_selected`; service `Describe`; the upgrade GET may still have used its HTTP binding |
 | Binary WebSocket message passes without a middleware RPC | Binary is unsupported by the V1 text-message binding under both `on_error` modes | `WEBSOCKET_MIDDLEWARE_COVERAGE state=unsupported_message_type`; the next text RPC may have a valid sequence gap |
 | WebSocket messages stop reaching middleware after one failure | A fail-open stage stream was disabled for the rest of the connection | `openshell.middleware.websocket_stage_disabled`; middleware timeout/stream/protocol logs. A per-message capacity bypass alone leaves the stage active. Reconnect to create a fresh stream after a genuine stream failure |

.agents/skills/generate-sandbox-policy/SKILL.md

@@ -83,7 +83,7 @@ Regardless of tier, extract (or infer) these from the user's description:
 | **Paths** | Specific URL paths or patterns | Only for custom/fine-grained |
 | **Enforcement** | `enforce` or `audit`? Default to `enforce`. | No — has a default |
 | **Binary** | Which binary/process should have access | Yes — ask if not stated |
-| **Middleware** | Whether admitted HTTP requests or client WebSocket text messages need an ordered built-in or operator-run processing stage | No |
+| **Middleware** | Whether admitted HTTP requests, final HTTP responses, or client WebSocket text messages need an ordered built-in or operator-run processing stage | No |
 
 If the host and access level are clear but binaries are not specified, ask the user which binary or process will be making the requests. Suggest common defaults like `/usr/bin/curl`, `/usr/local/bin/claude`, etc.
 
@@ -221,10 +221,12 @@ Is L7 inspection needed?
 
 ### Middleware Decision
 
-Add `network_middlewares` only when the user asks to inspect, transform, redact, or independently authorize admitted HTTP requests or client WebSocket text messages. Middleware runs after network and L7 policy admission and before provider credential injection.
+Add `network_middlewares` only when the user asks to inspect, transform, redact, or independently authorize admitted HTTP requests, final HTTP responses, or client WebSocket text messages. Request middleware runs after network and L7 policy admission and before provider credential injection. Response middleware runs after the upstream returns a final response and before OpenShell delivers it to the sandbox.
 
 - Use `openshell/regex` without gateway registration for fixed-pattern redaction of UTF-8 HTTP request bodies or complete client-to-upstream WebSocket text messages.
 - Use an operator-owned middleware name only when it is already registered under `[[openshell.supervisor.middleware]]` and reachable from both the gateway and sandbox supervisors.
+- Confirm that a requested response implementation exposes an `HTTP_RESPONSE/PRE_RETURN` binding. Choose `HEADERS_ONLY` for header-only processing, `WHOLE_BODY_BYTES` when the complete bounded body is required, or `STREAM_BYTES` for bounded lockstep units. V1 response middleware may transform permitted headers and body bytes but has no explicit body-denial decision.
+- A fail-closed response failure returns canonical `502 response_delivery_failed` before response commitment and aborts delivery after commitment. A fail-open stage is disabled and retained input continues through later stages; OpenShell emits a detection finding. Retrying an aborted response may repeat upstream side effects.
 - Confirm that a requested WebSocket implementation exposes a `WEBSOCKET_MESSAGE/PRE_CREDENTIALS` binding. `openshell/regex` exposes this binding. A host-matched HTTP-only implementation may inspect the upgrade GET but does not join the post-upgrade chain; messages pass and OpenShell emits `binding_not_selected` coverage regardless of `on_error`.
 - WebSocket middleware runs for both `ws://` and `wss://` and receives complete client text messages only. Binary messages pass under both error modes and emit `unsupported_message_type` coverage for active stages. Upstream-to-client messages remain uninspected. Do not claim that V1 provides all-message WebSocket inspection.
 - Treat `fail_open` on WebSocket as a session-scoped bypass: if the stage stream fails, OpenShell disables it for later messages on that connection and emits a state-change finding. Prefer `fail_closed` for required redaction or authorization.
@@ -391,6 +393,7 @@ Before presenting the policy to the user, verify correctness **and** flag breadt
 - [ ] Every middleware config has a non-empty `middleware` name and non-empty `endpoints.include`
 - [ ] Middleware `order` values are unique and no selected chain exceeds 10 stages
 - [ ] No fail-closed middleware selector can cover a `tls: skip` endpoint
+- [ ] Any required final-response control advertises `HTTP_RESPONSE/PRE_RETURN`, and its body mode and payload limit fit the intended response
 - [ ] Any required WebSocket control advertises `WEBSOCKET_MESSAGE/PRE_CREDENTIALS`, and the user understands that V1 does not inspect binary messages
 - [ ] Endpoints contributed by a credentialed provider are not L4-only or `tls: skip` unless `allow_uninspected_credentials: true` explicitly records the exception
 

.agents/skills/openshell-cli/SKILL.md

@@ -453,11 +453,11 @@ Edit `current-policy.yaml` to allow the blocked actions. **For policy content au
 - TLS termination configuration
 - Enforcement modes (`audit` vs `enforce`)
 - Binary matching patterns
-- Ordered `network_middlewares`, host selection, HTTP and WebSocket bindings, and `fail_open` or `fail_closed` behavior
+- Ordered `network_middlewares`, host selection, HTTP request, HTTP response, and WebSocket bindings, and `fail_open` or `fail_closed` behavior
 
 `network_policies` and `network_middlewares` can be modified at runtime when the selected compute driver supports live policy updates. MXC rejects live policy replacement and merge updates; delete and recreate an MXC sandbox instead. If `filesystem_policy`, `landlock`, or `process` need changes, the sandbox must be recreated. Built-in middleware such as `openshell/regex` needs no gateway registration. An operator-run middleware must already be registered under `[[openshell.supervisor.middleware]]`; changing that static registration requires a gateway restart.
 
-Middleware can inspect parsed HTTP request bodies and complete client-to-upstream WebSocket text messages over both `ws://` and `wss://` when the implementation advertises the matching binding. The built-in `openshell/regex` advertises both bindings and applies its fixed patterns to UTF-8 text. A host-matched HTTP-only attachment can inspect the upgrade GET but does not join the WebSocket chain; look for `binding_not_selected` coverage. Binary messages pass under both `on_error` modes and active stages emit `unsupported_message_type` coverage; upstream-to-client messages remain uninspected. A broken fail-open WebSocket stage is disabled for the rest of that connection; inspect sandbox OCSF logs for `openshell.middleware.websocket_stage_disabled`.
+Middleware can inspect parsed HTTP request bodies, final HTTP responses, and complete client-to-upstream WebSocket text messages when the implementation advertises the matching binding. Response middleware uses `HTTP_RESPONSE/PRE_RETURN` and selects `HEADERS_ONLY`, bounded `WHOLE_BODY_BYTES`, or bounded `STREAM_BYTES` during preflight. A fail-closed response failure returns canonical `502 response_delivery_failed` before commitment and aborts delivery after commitment; fail-open disables the failed stage, continues with retained input, and emits a detection finding. The built-in `openshell/regex` applies its fixed patterns to UTF-8 request bodies and WebSocket text messages. A host-matched HTTP-only attachment can inspect the upgrade GET but does not join the WebSocket chain; look for `binding_not_selected` coverage. Binary messages pass under both `on_error` modes and active stages emit `unsupported_message_type` coverage; upstream-to-client messages remain uninspected. A broken fail-open WebSocket stage is disabled for the rest of that connection; inspect sandbox OCSF logs for `openshell.middleware.websocket_stage_disabled`.
 
 ### Step 5: Push the updated policy