feat(claude): add forward_host_credentials support

Reads the host's Claude OAuth session key from ~/.claude.json at launch
and forwards it only to the egress sidecar (never to the agent), placing
a placeholder CLAUDE_CODE_OAUTH_TOKEN in the agent env so Claude Code
starts without seeing the real credential.

Mirrors the existing Codex forward_host_credentials flow (PRD 0029).
Adds claude_auth.py to extract and validate the sessionKey, a
CLAUDE_HOST_CREDENTIAL_TOKEN_REF constant in egress.py, and updates
manifest_agent.py to allow the flag for both 'codex' and 'claude'
templates. Also adds a mutual-exclusion check that rejects setting
both auth_token and forward_host_credentials together.

Co-Authored-By: Claude Sonnet 4.6 <noreply@anthropic.com>

fix(claude): read credentials from ~/.claude/.credentials.json

The actual OAuth token is in ~/.claude/.credentials.json under
claudeAiOauth.accessToken, not in ~/.claude.json.
~/.claude.json holds only UI state and profile metadata (oauthAccount
has no token fields). expiresAt in the credentials file is milliseconds,
not seconds.

Discovered after testing against Claude Code 2.1.198.

Co-Authored-By: Claude Sonnet 4.6 <noreply@anthropic.com>

fix(claude): fall back to macOS Keychain for credentials

On macOS, Claude Code stores credentials in the Keychain under
service "Claude Code-credentials" rather than in a file. When
~/.claude/.credentials.json is absent, shell out to:
  security find-generic-password -s "Claude Code-credentials" -w
and parse the result as the same JSON schema.

~/.claude.json holds only profile/UI metadata (oauthAccount has
no token fields). expiresAt in the credentials is milliseconds.

Co-Authored-By: Claude Sonnet 4.6 <noreply@anthropic.com>

docs(prd): fix credential path references (~/.claude/.credentials.json)

fix(test): suppress gitleaks false positives on synthetic Claude tokens

bot_bottle/contrib/claude/claude_auth.py

@@ -0,0 +1,114 @@
+"""Host Claude auth helpers.
+
+Reads the host's Claude Code credentials and returns only the access
+token needed by egress. Does not expose refresh tokens or raw payloads.
+
+Credential storage by platform:
+  Linux  — ~/.claude/.credentials.json
+  macOS  — macOS Keychain, service "Claude Code-credentials"
+            (file path is tried first; Keychain is the fallback)
+"""
+
+from __future__ import annotations
+
+import json
+import os
+import subprocess
+import sys
+from datetime import datetime, timezone
+from pathlib import Path
+
+from ...log import die
+
+
+_KEYCHAIN_SERVICE = "Claude Code-credentials"
+
+
+def claude_auth_path(host_env: dict[str, str] | None = None) -> Path:
+    env = os.environ if host_env is None else host_env
+    home = env.get("HOME")
+    if home:
+        return Path(home) / ".claude" / ".credentials.json"
+    return Path.home() / ".claude" / ".credentials.json"
+
+
+def _read_keychain() -> dict[str, object] | None:
+    """Try the macOS Keychain. Returns parsed JSON dict or None."""
+    if sys.platform != "darwin":
+        return None
+    try:
+        result = subprocess.run(
+            ["security", "find-generic-password", "-s", _KEYCHAIN_SERVICE, "-w"],
+            capture_output=True,
+            text=True,
+            timeout=10,
+        )
+    except (FileNotFoundError, subprocess.TimeoutExpired):
+        return None
+    if result.returncode != 0 or not result.stdout.strip():
+        return None
+    try:
+        raw = json.loads(result.stdout.strip())
+    except json.JSONDecodeError:
+        return None
+    return raw if isinstance(raw, dict) else None
+
+
+def claude_host_access_token(
+    host_env: dict[str, str] | None = None,
+    *,
+    now: datetime | None = None,
+) -> str:
+    path = claude_auth_path(host_env)
+    raw: dict[str, object] | None = None
+
+    if path.is_file():
+        try:
+            raw = json.loads(path.read_text())
+        except (OSError, json.JSONDecodeError) as e:
+            die(f"claude host credentials: could not read valid JSON at {path}: {e}")
+        if not isinstance(raw, dict):
+            die(f"claude host credentials: {path} must contain a JSON object")
+    else:
+        raw = _read_keychain()
+        if raw is None:
+            die(
+                f"claude host credentials: auth file missing at {path} and "
+                f"macOS Keychain lookup for '{_KEYCHAIN_SERVICE}' failed. "
+                "Run `claude login` on the host or disable "
+                "agent_provider.forward_host_credentials."
+            )
+
+    oauth = raw.get("claudeAiOauth")
+    if not isinstance(oauth, dict):
+        die(
+            "claude host credentials: claudeAiOauth is missing from credentials. "
+            "Run `claude login` on the host or disable "
+            "agent_provider.forward_host_credentials."
+        )
+
+    access_token = oauth.get("accessToken")
+    if not isinstance(access_token, str) or not access_token:
+        die(
+            "claude host credentials: claudeAiOauth.accessToken is missing or empty. "
+            "Run `claude login` on the host and restart the bottle."
+        )
+
+    # expiresAt is in milliseconds
+    expires_at = oauth.get("expiresAt")
+    if isinstance(expires_at, (int, float)):
+        check_now = now or datetime.now(timezone.utc)
+        exp_dt = datetime.fromtimestamp(float(expires_at) / 1000.0, timezone.utc)
+        if exp_dt <= check_now:
+            die(
+                "claude host credentials: host Claude access token is expired. "
+                "Run `claude login` on the host and restart the bottle."
+            )
+
+    return access_token
+
+
+__all__ = [
+    "claude_auth_path",
+    "claude_host_access_token",
+]