fix: Nous Portal rate limit guard — prevent retry amplification (#10568)

When Nous returns a 429, the retry amplification chain burns up to 9
API requests per conversation turn (3 SDK retries × 3 Hermes retries),
each counting against RPH and deepening the rate limit. With multiple
concurrent sessions (cron + gateway + auxiliary), this creates a spiral
where retries keep the limit tapped indefinitely.

New module: agent/nous_rate_guard.py
- Shared file-based rate limit state (~/.hermes/rate_limits/nous.json)
- Parses reset time from x-ratelimit-reset-requests-1h, x-ratelimit-
  reset-requests, retry-after headers, or error context
- Falls back to 5-minute default cooldown if no header data
- Atomic writes (tempfile + rename) for cross-process safety
- Auto-cleanup of expired state files

run_agent.py changes:
- Top-of-retry-loop guard: when another session already recorded Nous
  as rate-limited, skip the API call entirely. Try fallback provider
  first, then return a clear message with the reset time.
- On 429 from Nous: record rate limit state and skip further retries
  (sets retry_count = max_retries to trigger fallback path)
- On success from Nous: clear the rate limit state so other sessions
  know they can resume

auxiliary_client.py changes:
- _try_nous() checks rate guard before attempting Nous in the auxiliary
  fallback chain. When rate-limited, returns (None, None) so the chain
  skips to the next provider instead of piling more requests onto Nous.

This eliminates three sources of amplification:
1. Hermes-level retries (saves 6 of 9 calls per turn)
2. Cross-session retries (cron + gateway all skip Nous)
3. Auxiliary fallback to Nous (compression/session_search skip too)

Includes 24 tests covering the rate guard module, header parsing,
state lifecycle, and auxiliary client integration.

agent/auxiliary_client.py

@@ -775,6 +775,21 @@ def _try_openrouter() -> Tuple[Optional[OpenAI], Optional[str]]:
 
 
 def _try_nous(vision: bool = False) -> Tuple[Optional[OpenAI], Optional[str]]:
+    # Check cross-session rate limit guard before attempting Nous —
+    # if another session already recorded a 429, skip Nous entirely
+    # to avoid piling more requests onto the tapped RPH bucket.
+    try:
+        from agent.nous_rate_guard import nous_rate_limit_remaining
+        _remaining = nous_rate_limit_remaining()
+        if _remaining is not None and _remaining > 0:
+            logger.debug(
+                "Auxiliary: skipping Nous Portal (rate-limited, resets in %.0fs)",
+                _remaining,
+            )
+            return None, None
+    except Exception:
+        pass
+
     nous = _read_nous_auth()
     if not nous:
         return None, None

agent/nous_rate_guard.py

@@ -0,0 +1,182 @@
+"""Cross-session rate limit guard for Nous Portal.
+
+Writes rate limit state to a shared file so all sessions (CLI, gateway,
+cron, auxiliary) can check whether Nous Portal is currently rate-limited
+before making requests.  Prevents retry amplification when RPH is tapped.
+
+Each 429 from Nous triggers up to 9 API calls per conversation turn
+(3 SDK retries x 3 Hermes retries), and every one of those calls counts
+against RPH.  By recording the rate limit state on first 429 and checking
+it before subsequent attempts, we eliminate the amplification effect.
+"""
+
+from __future__ import annotations
+
+import json
+import logging
+import os
+import tempfile
+import time
+from typing import Any, Mapping, Optional
+
+logger = logging.getLogger(__name__)
+
+_STATE_SUBDIR = "rate_limits"
+_STATE_FILENAME = "nous.json"
+
+
+def _state_path() -> str:
+    """Return the path to the Nous rate limit state file."""
+    try:
+        from hermes_constants import get_hermes_home
+        base = get_hermes_home()
+    except ImportError:
+        base = os.path.join(os.path.expanduser("~"), ".hermes")
+    return os.path.join(base, _STATE_SUBDIR, _STATE_FILENAME)
+
+
+def _parse_reset_seconds(headers: Optional[Mapping[str, str]]) -> Optional[float]:
+    """Extract the best available reset-time estimate from response headers.
+
+    Priority:
+      1. x-ratelimit-reset-requests-1h  (hourly RPH window — most useful)
+      2. x-ratelimit-reset-requests     (per-minute RPM window)
+      3. retry-after                     (generic HTTP header)
+
+    Returns seconds-from-now, or None if no usable header found.
+    """
+    if not headers:
+        return None
+
+    lowered = {k.lower(): v for k, v in headers.items()}
+
+    for key in (
+        "x-ratelimit-reset-requests-1h",
+        "x-ratelimit-reset-requests",
+        "retry-after",
+    ):
+        raw = lowered.get(key)
+        if raw is not None:
+            try:
+                val = float(raw)
+                if val > 0:
+                    return val
+            except (TypeError, ValueError):
+                pass
+
+    return None
+
+
+def record_nous_rate_limit(
+    *,
+    headers: Optional[Mapping[str, str]] = None,
+    error_context: Optional[dict[str, Any]] = None,
+    default_cooldown: float = 300.0,
+) -> None:
+    """Record that Nous Portal is rate-limited.
+
+    Parses the reset time from response headers or error context.
+    Falls back to ``default_cooldown`` (5 minutes) if no reset info
+    is available.  Writes to a shared file that all sessions can read.
+
+    Args:
+        headers: HTTP response headers from the 429 error.
+        error_context: Structured error context from _extract_api_error_context().
+        default_cooldown: Fallback cooldown in seconds when no header data.
+    """
+    now = time.time()
+    reset_at = None
+
+    # Try headers first (most accurate)
+    header_seconds = _parse_reset_seconds(headers)
+    if header_seconds is not None:
+        reset_at = now + header_seconds
+
+    # Try error_context reset_at (from body parsing)
+    if reset_at is None and isinstance(error_context, dict):
+        ctx_reset = error_context.get("reset_at")
+        if isinstance(ctx_reset, (int, float)) and ctx_reset > now:
+            reset_at = float(ctx_reset)
+
+    # Default cooldown
+    if reset_at is None:
+        reset_at = now + default_cooldown
+
+    path = _state_path()
+    try:
+        state_dir = os.path.dirname(path)
+        os.makedirs(state_dir, exist_ok=True)
+
+        state = {
+            "reset_at": reset_at,
+            "recorded_at": now,
+            "reset_seconds": reset_at - now,
+        }
+
+        # Atomic write: write to temp file + rename
+        fd, tmp_path = tempfile.mkstemp(dir=state_dir, suffix=".tmp")
+        try:
+            with os.fdopen(fd, "w") as f:
+                json.dump(state, f)
+            os.replace(tmp_path, path)
+        except Exception:
+            # Clean up temp file on failure
+            try:
+                os.unlink(tmp_path)
+            except OSError:
+                pass
+            raise
+
+        logger.info(
+            "Nous rate limit recorded: resets in %.0fs (at %.0f)",
+            reset_at - now, reset_at,
+        )
+    except Exception as exc:
+        logger.debug("Failed to write Nous rate limit state: %s", exc)
+
+
+def nous_rate_limit_remaining() -> Optional[float]:
+    """Check if Nous Portal is currently rate-limited.
+
+    Returns:
+        Seconds remaining until reset, or None if not rate-limited.
+    """
+    path = _state_path()
+    try:
+        with open(path) as f:
+            state = json.load(f)
+        reset_at = state.get("reset_at", 0)
+        remaining = reset_at - time.time()
+        if remaining > 0:
+            return remaining
+        # Expired — clean up
+        try:
+            os.unlink(path)
+        except OSError:
+            pass
+        return None
+    except (FileNotFoundError, json.JSONDecodeError, KeyError, TypeError):
+        return None
+
+
+def clear_nous_rate_limit() -> None:
+    """Clear the rate limit state (e.g., after a successful Nous request)."""
+    try:
+        os.unlink(_state_path())
+    except FileNotFoundError:
+        pass
+    except OSError as exc:
+        logger.debug("Failed to clear Nous rate limit state: %s", exc)
+
+
+def format_remaining(seconds: float) -> str:
+    """Format seconds remaining into human-readable duration."""
+    s = max(0, int(seconds))
+    if s < 60:
+        return f"{s}s"
+    if s < 3600:
+        m, sec = divmod(s, 60)
+        return f"{m}m {sec}s" if sec else f"{m}m"
+    h, remainder = divmod(s, 3600)
+    m = remainder // 60
+    return f"{h}h {m}m" if m else f"{h}h"