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>

tests/unit/test_agent_provider.py

@@ -9,11 +9,15 @@ import unittest
 from pathlib import Path
 
 from bot_bottle.agent_provider import (
+    CLAUDE_HOST_CREDENTIAL_HOSTS,
     CODEX_HOST_CREDENTIAL_HOSTS,
     build_agent_provision_plan,
     prompt_args,
 )
-from bot_bottle.egress import CODEX_HOST_CREDENTIAL_TOKEN_REF
+from bot_bottle.egress import (
+    CLAUDE_HOST_CREDENTIAL_TOKEN_REF,
+    CODEX_HOST_CREDENTIAL_TOKEN_REF,
+)
 
 
 def _jwt(exp: int) -> str:
@@ -289,6 +293,65 @@ class TestAgentProviderRuntime(unittest.TestCase):
             )
         self.assertEqual({}, plan.provisioned_env)
 
+    def test_claude_forward_host_credentials_populates_egress_route(self):
+        session_key = "sk-ant-oat01-test-key"
+        with tempfile.TemporaryDirectory(prefix="bb-provider.") as tmp:
+            home = Path(tmp) / "host-claude"
+            home.mkdir()
+            (home / ".claude.json").write_text(json.dumps({
+                "oauthAccount": {"sessionKey": session_key},
+            }))
+            plan = build_agent_provision_plan(
+                template="claude",
+                dockerfile="",
+                state_dir=Path(tmp),
+                instance_name="bot-bottle-test",
+                prompt_file=Path(tmp) / "prompt.txt",
+                forward_host_credentials=True,
+                host_env={"HOME": str(home)},
+            )
+        self.assertEqual(1, len(plan.egress_routes))
+        route = plan.egress_routes[0]
+        self.assertIn(route.host, CLAUDE_HOST_CREDENTIAL_HOSTS)
+        self.assertEqual("Bearer", route.auth_scheme)
+        self.assertEqual(CLAUDE_HOST_CREDENTIAL_TOKEN_REF, route.token_ref)
+        self.assertEqual("egress-placeholder", plan.env_vars["CLAUDE_CODE_OAUTH_TOKEN"])
+        self.assertEqual(frozenset({"CLAUDE_CODE_OAUTH_TOKEN"}), plan.hidden_env_names)
+
+    def test_claude_forward_host_credentials_populates_provisioned_env(self):
+        session_key = "sk-ant-oat01-test-key"
+        with tempfile.TemporaryDirectory(prefix="bb-provider.") as tmp:
+            home = Path(tmp) / "host-claude"
+            home.mkdir()
+            (home / ".claude.json").write_text(json.dumps({
+                "oauthAccount": {"sessionKey": session_key},
+            }))
+            plan = build_agent_provision_plan(
+                template="claude",
+                dockerfile="",
+                state_dir=Path(tmp),
+                instance_name="bot-bottle-test",
+                prompt_file=Path(tmp) / "prompt.txt",
+                forward_host_credentials=True,
+                host_env={"HOME": str(home)},
+            )
+        self.assertEqual(
+            {CLAUDE_HOST_CREDENTIAL_TOKEN_REF: session_key},
+            plan.provisioned_env,
+        )
+
+    def test_claude_without_forward_host_credentials_has_empty_provisioned_env(self):
+        with tempfile.TemporaryDirectory(prefix="bb-provider.") as tmp:
+            plan = build_agent_provision_plan(
+                template="claude",
+                dockerfile="",
+                state_dir=Path(tmp),
+                instance_name="bot-bottle-test",
+                prompt_file=Path(tmp) / "prompt.txt",
+                forward_host_credentials=False,
+            )
+        self.assertEqual({}, plan.provisioned_env)
+
     def test_pi_plan_writes_default_ollama_models(self):
         with tempfile.TemporaryDirectory(prefix="bb-provider.") as tmp:
             plan = build_agent_provision_plan(