feat(security): enable secret redaction by default (#17691, #20785) (#21193)

Flip the default for HERMES_REDACT_SECRETS from off to on so the redactor
already wired into send_message_tool, logs, and tool output actually runs
on a fresh install.

- agent/redact.py: env-var default "" → "true"
- hermes_cli/config.py: DEFAULT_CONFIG security.redact_secrets True;
  two config-template comments rewritten
- gateway/run.py + cli.py: startup log / banner warning when the user
  has explicitly opted out, so the downgrade is visible in agent.log
  and at CLI banner time
- docs/reference/environment-variables.md: description reconciled
- tests: flipped the default-pin, restructured the force=True
  regression test to explicit-false instead of unset

Users who need raw credential values (redactor development) can still
opt out via security.redact_secrets: false in config.yaml or
HERMES_REDACT_SECRETS=false in .env.

Closes #17691.
Addresses #20785 (short-term output-pipeline recommendation).

gateway/run.py

@@ -2860,6 +2860,29 @@ class GatewayRunner:
             )
         except Exception:
             pass
+        # Redaction status: ON by default (#17691). Surface a prominent
+        # warning if an operator has explicitly opted out so they don't
+        # forget the downgrade is active — the redactor snapshots its
+        # state at import time, so this log line is the source of truth
+        # for this process's lifetime.
+        try:
+            _redact_raw = os.getenv("HERMES_REDACT_SECRETS", "true")
+            _redact_on = _redact_raw.lower() in ("1", "true", "yes", "on")
+            if _redact_on:
+                logger.info(
+                    "Secret redaction: ENABLED (tool output, logs, and chat "
+                    "responses are scrubbed before delivery)"
+                )
+            else:
+                logger.warning(
+                    "Secret redaction: DISABLED (HERMES_REDACT_SECRETS=%s). "
+                    "API keys and tokens may appear verbatim in chat output, "
+                    "session JSONs, and logs. Set security.redact_secrets: true "
+                    "in config.yaml to re-enable.",
+                    _redact_raw,
+                )
+        except Exception:
+            pass
         try:
             from hermes_cli.profiles import get_active_profile_name
             _profile = get_active_profile_name()