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/help/environment.md

@@ -56,6 +56,18 @@ Env var equivalents:
 - `OPENCLAW_LOAD_SHELL_ENV=1`
 - `OPENCLAW_SHELL_ENV_TIMEOUT_MS=15000`
 
+## Runtime-injected env vars
+
+OpenClaw also injects context markers into spawned child processes:
+
+- `OPENCLAW_SHELL=exec`: set for commands run through the `exec` tool.
+- `OPENCLAW_SHELL=acp`: set for ACP runtime backend process spawns (for example `acpx`).
+- `OPENCLAW_SHELL=acp-client`: set for `openclaw acp client` when it spawns the ACP bridge process.
+- `OPENCLAW_SHELL=tui-local`: set for local TUI `!` shell commands.
+
+These are runtime markers (not required user config). They can be used in shell/profile logic
+to apply context-specific rules.
+
 ## Env var substitution in config
 
 You can reference env vars directly in config string values using `${VAR_NAME}` syntax: