fix: cap pending process output

docs/gateway/background-process.md

@@ -33,6 +33,7 @@ When spawning long-running child processes outside the exec/process tools (for e
 Environment overrides:
 - `PI_BASH_YIELD_MS`: default yield (ms)
 - `PI_BASH_MAX_OUTPUT_CHARS`: in‑memory output cap (chars)
+- `CLAWDBOT_BASH_PENDING_MAX_OUTPUT_CHARS`: pending stdout/stderr cap per stream (chars)
 - `PI_BASH_JOB_TTL_MS`: TTL for finished sessions (ms, bounded to 1m–3h)
 
 Config (preferred):