feat: era-rollup + narrative engine (consolidation steps 3-4)

Complete the consolidation pipeline: summaries -> profile + eras -> narrative.

- memory: eras table (per-month digests) + Era, summaries_by_month, store_era,
  list_eras, recall_eras; narrative table + set/get_narrative
- lyra/era.py (lyra-era): groups session gists by the month the session occurred
  (real timestamps) and map-reduces each month into a "what was happening" digest
- lyra/narrative.py (lyra-narrative): distills profile + recent eras into the
  current arc/trends/callbacks ("remember when…", "you're trending toward…")
- chat.build_messages injects the narrative alongside the profile

Verified on the real corpus: 17 monthly eras (Dec 2024-Jun 2026) + a narrative
that surfaces specific callbacks (the $573 Hollywood session, 4 years sober).

Co-Authored-By: Claude Opus 4.8 (1M context) <noreply@anthropic.com>

lyra/narrative.py

@@ -0,0 +1,66 @@
+"""Narrative engine (consolidation step 4): the current arc, trends, callbacks.
+
+Where the profile is timeless ("who Brian is"), the narrative is time-aware
+("what's going on lately, where things are trending"). It distills the profile
+plus the most recent monthly era digests into the current story — recent focus,
+notable trends or changes, mood/arc, and a few specific callbacks worth
+referencing. Injected into chat so Lyra follows along like a friend who's been
+paying attention. Runs on the consolidation backend (MI50 in steady state).
+"""
+from __future__ import annotations
+
+
+from lyra import config, llm, logbus, memory
+from lyra.llm import Backend, Message
+
+RECENT_ERAS = 4
+
+_PROMPT = """You are distilling the CURRENT narrative about Brian — what a close \
+friend who has been following along would keep in mind right now. From his profile \
+and recent monthly digests below, write: what he's been focused on lately, any \
+notable trends or changes (improving, slipping, new patterns), his current arc and \
+mood, and 2-4 specific things worth referencing back to him ("remember when…"). \
+Third person, referring to him as "Brian". 6-10 sentences. This is a memory note, \
+not a reply. No preamble."""
+
+
+def rebuild_narrative(backend: Backend | None = None) -> str | None:
+    """(Re)derive the current narrative from the profile + recent era digests."""
+    backend = backend or config.load().summary_backend
+    profile = memory.get_profile()
+    eras = memory.list_eras()
+    if not profile and not eras:
+        return None
+
+    parts = []
+    if profile:
+        parts.append("PROFILE (timeless):\n" + profile)
+    recent = eras[-RECENT_ERAS:]
+    if recent:
+        parts.append(
+            "RECENT MONTHS (oldest first):\n"
+            + "\n\n".join(f"[{e.month}]\n{e.content}" for e in recent)
+        )
+    body = "\n\n".join(parts)
+
+    messages: list[Message] = [
+        {"role": "system", "content": _PROMPT},
+        {"role": "user", "content": body},
+    ]
+    narrative = llm.complete(messages, backend=backend)
+    memory.set_narrative(narrative)
+    logbus.log("info", "narrative rebuilt", chars=len(narrative), eras=len(recent))
+    return narrative
+
+
+def main() -> int:
+    narrative = rebuild_narrative()
+    if narrative is None:
+        print("Need a profile and/or eras first — run lyra-profile and lyra-era.")
+        return 1
+    print(narrative)
+    return 0
+
+
+if __name__ == "__main__":
+    raise SystemExit(main())