fix(gateway/webhook): don't pop delivery_info on send

The webhook adapter stored per-request `deliver`/`deliver_extra` config in
`_delivery_info[chat_id]` during POST handling and consumed it via `.pop()`
inside `send()`. That worked for routes whose agent run produced exactly
one outbound message — the final response — but it broke whenever the
agent emitted any interim status message before the final response.

Status messages flow through the same `send(chat_id, ...)` path as the
final response (see `gateway/run.py::_status_callback_sync` →
`adapter.send(...)`). Common triggers include:

  - "🔄 Primary model failed — switching to fallback: ..."
    (run_agent.py::_emit_status when `fallback_providers` activates)
  - context-pressure / compression notices
  - any other lifecycle event routed through `status_callback`

When any of those fired, the first `send()` call popped the entry, so the
subsequent final-response `send()` saw an empty dict and silently
downgraded `deliver_type` from `"telegram"` (or `discord`/`slack`/etc.) to
the default `"log"`. The agent's response was logged to the gateway log
instead of being delivered to the configured cross-platform target — no
warning, no error, just a missing message.

This was easy to hit in practice. Any user with `fallback_providers`
configured saw it the first time their primary provider hiccuped on a
webhook-triggered run. Routes that worked perfectly in dev (where the
primary stays healthy) silently dropped responses in prod.

Fix: read `_delivery_info` with `.get()` so multiple `send()` calls for
the same `chat_id` all see the same delivery config. To keep the dict
bounded without relying on per-send cleanup, add a parallel
`_delivery_info_created` timestamp dict and a `_prune_delivery_info()`
helper that drops entries older than `_idempotency_ttl` (1h, same window
already used by `_seen_deliveries`). Pruning runs on each POST, mirroring
the existing `_seen_deliveries` cleanup pattern.

Worst-case memory footprint is now `rate_limit * TTL = 30/min * 60min =
1800` entries, each ~1KB → under 2 MB. In practice it'll be far smaller
because most webhooks complete in seconds, not the full hour.

Test changes:
  - `test_delivery_info_cleaned_after_send` is replaced with
    `test_delivery_info_survives_multiple_sends`, which is now the
    regression test for this bug — it asserts that two consecutive
    `send()` calls both see the delivery config.
  - A new `test_delivery_info_pruned_via_ttl` covers the TTL cleanup
    behavior.
  - The two integration tests that asserted `chat_id not in
    adapter._delivery_info` after `send()` now assert the opposite, with
    a comment explaining why.

All 40 tests in `tests/gateway/test_webhook_adapter.py` and
`tests/gateway/test_webhook_integration.py` pass. Verified end-to-end
locally against a dynamic `hermes webhook subscribe` route configured
with `--deliver telegram --deliver-chat-id <user>`: with `gpt-5.4` as
the primary (currently flaky) and `claude-opus-4.6` as the fallback,
the fallback notification fires, the agent finishes, and the final
response is delivered to Telegram as expected.

tests/gateway/test_webhook_adapter.py

@@ -590,8 +590,15 @@ class TestSessionIsolation:
 class TestDeliveryCleanup:
 
     @pytest.mark.asyncio
-    async def test_delivery_info_cleaned_after_send(self):
-        """send() pops delivery_info so the entry doesn't leak memory."""
+    async def test_delivery_info_survives_multiple_sends(self):
+        """send() must NOT pop delivery_info.
+
+        Interim status messages (fallback notifications, context-pressure
+        warnings, etc.) flow through the same send() path as the final
+        response.  If the entry were popped on the first send, the final
+        response would silently downgrade to the ``log`` deliver type.
+        Regression test for that bug.
+        """
         adapter = _make_adapter()
         chat_id = "webhook:test:d-xyz"
         adapter._delivery_info[chat_id] = {
@@ -599,10 +606,40 @@ class TestDeliveryCleanup:
             "deliver_extra": {},
             "payload": {"x": 1},
         }
+        adapter._delivery_info_created[chat_id] = time.time()
 
-        result = await adapter.send(chat_id, "Agent response here")
-        assert result.success is True
-        assert chat_id not in adapter._delivery_info
+        # First send (e.g. an interim status message)
+        result1 = await adapter.send(chat_id, "Status: switching to fallback")
+        assert result1.success is True
+        # Entry must still be present so the final send can read it
+        assert chat_id in adapter._delivery_info
+
+        # Second send (the final agent response)
+        result2 = await adapter.send(chat_id, "Final agent response")
+        assert result2.success is True
+        assert chat_id in adapter._delivery_info
+
+    @pytest.mark.asyncio
+    async def test_delivery_info_pruned_via_ttl(self):
+        """Stale delivery_info entries are dropped on the next POST."""
+        adapter = _make_adapter()
+        adapter._idempotency_ttl = 60  # short TTL for the test
+        now = time.time()
+
+        # Stale entry — older than TTL
+        adapter._delivery_info["webhook:test:old"] = {"deliver": "log"}
+        adapter._delivery_info_created["webhook:test:old"] = now - 120
+
+        # Fresh entry — should survive
+        adapter._delivery_info["webhook:test:new"] = {"deliver": "log"}
+        adapter._delivery_info_created["webhook:test:new"] = now - 5
+
+        adapter._prune_delivery_info(now)
+
+        assert "webhook:test:old" not in adapter._delivery_info
+        assert "webhook:test:old" not in adapter._delivery_info_created
+        assert "webhook:test:new" in adapter._delivery_info
+        assert "webhook:test:new" in adapter._delivery_info_created
 
 
 # ===================================================================

tests/gateway/test_webhook_integration.py

@@ -259,8 +259,9 @@ class TestCrossPlatformDelivery:
         mock_tg_adapter.send.assert_awaited_once_with(
             "12345", "I've acknowledged the alert.", metadata=None
         )
-        # Delivery info should be cleaned up
-        assert chat_id not in adapter._delivery_info
+        # Delivery info is retained after send() so interim status messages
+        # don't strand the final response (TTL-based cleanup happens on POST).
+        assert chat_id in adapter._delivery_info
 
 
 # ===================================================================
@@ -333,5 +334,6 @@ class TestGitHubCommentDelivery:
             text=True,
             timeout=30,
         )
-        # Delivery info cleaned up
-        assert chat_id not in adapter._delivery_info
+        # Delivery info is retained after send() so interim status messages
+        # don't strand the final response (TTL-based cleanup happens on POST).
+        assert chat_id in adapter._delivery_info