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).

hermes_cli/config.py

@@ -1191,7 +1191,7 @@ DEFAULT_CONFIG = {
     # Pre-exec security scanning via tirith
     "security": {
         "allow_private_urls": False,  # Allow requests to private/internal IPs (for OpenWrt, proxies, VPNs)
-        "redact_secrets": False,
+        "redact_secrets": True,
         "tirith_enabled": True,
         "tirith_path": "tirith",
         "tirith_timeout": 5,
@@ -3978,10 +3978,10 @@ def load_config() -> Dict[str, Any]:
 
 _SECURITY_COMMENT = """
 # ── Security ──────────────────────────────────────────────────────────
-# Secret redaction is OFF by default — tool output (terminal stdout,
-# read_file results, web content) passes through unmodified. Set
-# redact_secrets to true to mask strings that look like API keys, tokens,
-# and passwords before they enter the model context and logs.
+# Secret redaction is ON by default — strings that look like API keys,
+# tokens, and passwords are masked in tool output, logs, and chat
+# responses before the model or user ever sees them. Set redact_secrets
+# to false to disable (e.g. when developing the redactor itself).
 # tirith pre-exec scanning is enabled by default when the tirith binary
 # is available. Configure via security.tirith_* keys or env vars
 # (TIRITH_ENABLED, TIRITH_BIN, TIRITH_TIMEOUT, TIRITH_FAIL_OPEN).
@@ -4021,8 +4021,8 @@ _FALLBACK_COMMENT = """
 
 _COMMENTED_SECTIONS = """
 # ── Security ──────────────────────────────────────────────────────────
-# Secret redaction is OFF by default. Set to true to mask strings that
-# look like API keys, tokens, and passwords in tool output and logs.
+# Secret redaction is ON by default. Set to false to pass tool output,
+# logs, and chat responses through unmodified (e.g. for redactor dev).
 #
 # security:
 #   redact_secrets: true