feat(fable-mcp): add reset_today_briefing tool

Wipes today's briefing messages (keeps the conversation row) and
optionally re-fires the compilation slot to regenerate. Pairs with
the new POST /api/briefing/reset-today backend route.

Also drops the stale briefing_mode reference from trigger_briefing's
docstring now that legacy mode is gone.

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

fable-mcp/fable_mcp/server.py

@@ -684,10 +684,9 @@ async def fable_trigger_briefing(slot: str = "compilation") -> dict:
     """Manually run a briefing slot for the current user.
 
     Fires the same data refresh the scheduler does (RSS, weather),
-    runs the briefing pipeline (legacy or agentic based on the user's
+    runs the agentic briefing pipeline, and writes the result into
-    ``briefing_mode`` setting), and writes the result into today's
+    today's briefing conversation. Use this to test prompt changes
-    briefing conversation. Use this to test prompt changes without
+    without waiting for the next scheduled slot.
-    waiting for the next scheduled slot.
 
     Args:
         slot: One of ``compilation`` (full morning, default), ``morning``,
@@ -699,6 +698,35 @@ async def fable_trigger_briefing(slot: str = "compilation") -> dict:
         return await briefing.trigger_briefing(client, slot=slot)
 
 
+@mcp.tool()
+async def fable_reset_today_briefing(run_compilation: bool = True) -> dict:
+    """Wipe today's briefing and (optionally) regenerate from scratch.
+
+    Deletes every message in today's briefing conversation — the
+    conversation row itself is kept so its id stays stable for any
+    open UI sessions. If ``run_compilation`` is True (the default),
+    immediately fires the compilation slot afterward so a fresh
+    briefing lands in place of the deleted content.
+
+    Use this when iterating on briefing prompts or tools and you want
+    to start from a clean slate rather than append another slot update
+    on top of stale output.
+
+    Args:
+        run_compilation: When True, fire ``POST /api/briefing/trigger``
+            for the ``compilation`` slot immediately after wiping.
+            Set False to only wipe without regenerating.
+
+    Returns a dict with ``reset`` (the delete result: deleted count +
+    conversation id) and ``triggered`` (the new message payload, or
+    null if regeneration was skipped).
+    """
+    async with FableClient() as client:
+        return await briefing.reset_today_briefing(
+            client, run_compilation=run_compilation,
+        )
+
+
 # ---------------------------------------------------------------------------
 # Generic conversation access
 # ---------------------------------------------------------------------------

fable-mcp/fable_mcp/tools/briefing.py

@@ -67,6 +67,26 @@ async def trigger_briefing(
     return await client.post("/api/briefing/trigger", json={"slot": slot})
 
 
+async def reset_today_briefing(
+    client: FableClient,
+    *,
+    run_compilation: bool = True,
+) -> dict[str, Any]:
+    """Delete all messages in today's briefing and optionally regenerate.
+
+    Wipes the messages in today's briefing conversation (keeping the
+    conversation row), then, if ``run_compilation`` is True, fires the
+    compilation slot so a fresh briefing lands in its place.
+    """
+    reset = await client.post("/api/briefing/reset-today")
+    if not run_compilation:
+        return {"reset": reset, "triggered": None}
+    triggered = await client.post(
+        "/api/briefing/trigger", json={"slot": "compilation"}
+    )
+    return {"reset": reset, "triggered": triggered}
+
+
 # ── Generic conversations ───────────────────────────────────────────────────
 
 async def get_conversation(