feat(orchestrator): update a single egress secret in place (0081)

Add a single-secret counterpart to reprovision_from_secret's restore-all:
update ONE egress token for a running bottle without a relaunch, for
refreshing a short-lived host credential (e.g. the Codex access token)
whose launch-time snapshot has expired.

- registry_store.store_agent_secret: per-key upsert (delete+insert of the
  one row), the counterpart of store_agent_secrets' replace-all.
- OrchestratorCore.update_agent_secret: set the in-memory token AND upsert
  the re-encrypted row under the bottle's env_var_secret, leaving other
  tokens untouched.
- POST /bottles/<id>/secret (cli-only) + client.update_agent_secret.

Refs #510, #512

Co-Authored-By: Claude Opus 4.8 <noreply@anthropic.com>

bot_bottle/orchestrator/api.py

@@ -50,6 +50,12 @@ class ReprovisionBody(_StrictModel):
     env_var_secret: StrictStr
 
 
+class SecretBody(_StrictModel):
+    name: StrictStr
+    value: StrictStr
+    env_var_secret: StrictStr
+
+
 class ReconcileBody(_StrictModel):
     live_source_ips: list[StrictStr]
     grace_seconds: float | None = None
@@ -259,6 +265,21 @@ def create_app(orch: OrchestratorCore, *, signing_key: str) -> FastAPI:
             return {"reprovisioned": True}
         raise HTTPException(404, "no stored secrets for this bottle")
 
+    @app.post("/bottles/{bottle_id}/secret")
+    def update_secret(bottle_id: str, body: SecretBody) -> dict[str, object]:
+        # Update ONE egress token for a running bottle in place — the
+        # single-secret form of reprovision, for refreshing a short-lived host
+        # credential (e.g. the Codex access token) without a relaunch. cli-only
+        # (not in _GATEWAY_ROUTES): a bottle must never set its own tokens.
+        if orch.update_agent_secret(
+            bottle_id,
+            _required(body.name, "name"),
+            _required(body.value, "value"),
+            _required(body.env_var_secret, "env_var_secret"),
+        ):
+            return {"updated": True}
+        raise HTTPException(404, "no such bottle")
+
     @app.delete("/bottles/{bottle_id}")
     def teardown(bottle_id: str) -> dict[str, object]:
         if orch.teardown_bottle(bottle_id):