Exec/ACP: inject OPENCLAW_SHELL into child shell env (#31271)

* exec: mark runtime shell context in exec env

* tests(exec): cover OPENCLAW_SHELL in gateway exec

* tests(exec): cover OPENCLAW_SHELL in pty mode

* acpx: mark runtime shell context for spawned process

* tests(acpx): log OPENCLAW_SHELL in runtime fixture

* tests(acpx): assert OPENCLAW_SHELL in runtime prompt

* docs(env): document OPENCLAW_SHELL runtime markers

* docs(exec): describe OPENCLAW_SHELL exec marker

* docs(acp): document OPENCLAW_SHELL acp marker

* docs(gateway): note OPENCLAW_SHELL for background exec

* tui: tag local shell runs with OPENCLAW_SHELL

* tests(tui): assert OPENCLAW_SHELL in local shell runner

* acp client: tag spawned bridge env with OPENCLAW_SHELL

* tests(acp): cover acp client OPENCLAW_SHELL env helper

* docs(env): include acp-client and tui-local shell markers

* docs(acp): document acp-client OPENCLAW_SHELL marker

* docs(tui): document tui-local OPENCLAW_SHELL marker

* exec: keep shell runtime env string-only for docker args

* changelog: note OPENCLAW_SHELL runtime markers

docs/cli/acp.md

@@ -179,6 +179,8 @@ Security note:
 
 - `--token` and `--password` can be visible in local process listings on some systems.
 - Prefer `--token-file`/`--password-file` or environment variables (`OPENCLAW_GATEWAY_TOKEN`, `OPENCLAW_GATEWAY_PASSWORD`).
+- ACP runtime backend child processes receive `OPENCLAW_SHELL=acp`, which can be used for context-specific shell/profile rules.
+- `openclaw acp client` sets `OPENCLAW_SHELL=acp-client` on the spawned bridge process.
 
 ### `acp client` options