Merge remote-tracking branch 'origin/master' into codex/skill-system

# Conflicts:
#	docs/rfc/INDEX.md
#	examples/acp-agent/tests/snapshots/both-mode-turn/session.jsonl
#	examples/acp-agent/tests/snapshots/code-mode-turn/session.jsonl
#	examples/acp-agent/tests/snapshots/text-turn/session.jsonl
#	packages/README.md

docs/architecture.md

@@ -26,6 +26,7 @@ Composition is preferred over inheritance. `packages/core/` is a repository grou
 |---|---|---|
 | `ctx.llm` | [`llm/`](../packages/llm/README.md) | adapter registry and streaming model calls |
 | `ctx.bash` | [`bash/`](../packages/bash/README.md) | foreground/background command execution |
+| `ctx.sandbox` | [`sandbox/`](../packages/sandbox/README.md) | same-world process confinement (argv wrapping, per-call policy) |
 | `ctx.codeRuntime` | [`code-runtime/`](../packages/code-runtime/README.md) | model-written program execution |
 | `ctx.fs` | [`fs/`](../packages/fs/README.md) | filesystem provider primitives and policy events |
 | `ctx.skills` | [`skill/`](../packages/skill/README.md) | skill provider registry and progressive disclosure |
@@ -144,6 +145,7 @@ New behavior should attach to a documented extension point; changing the shipped
 | Add a model-facing capability | register a tool on `ctx.tools`; schemas flow into prompt assembly |
 | Add command execution | implement and register a `ctx.bash` backend |
 | Add filesystem access or policy | implement a `ctx.fs` provider or listen on `fs/*` policy events |
+| Confine spawned processes | a `ctx.sandbox` backend; consumers wrap their argv before spawning |
 | Intercept prompts, requests, tool use, or continuation | listen on the relevant `agent/*` or `tools/*` waterfall |
 | Add a session-stable request prefix outside history | compose it on `agent/session-prefix`, once per loop instance; logged on the request header |
 | Add UI or editor integration | drive `ctx.agents` and render from `session/event` |