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/era.py

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+"""Era rollups: per-month "what was happening" digests (consolidation step 3).
+
+Groups session gists by the calendar month the session occurred (from real
+exchange timestamps) and map-reduces each month into one digest. These are the
+temporal memory tier — they answer "what was going on last December" and feed
+the narrative engine. 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
+
+BATCH_CHARS = 18000
+
+_PROMPT = """You are writing a monthly memory digest about Brian from the session \
+summaries below (all from the same month). Capture: what he was focused on (poker \
+and otherwise), notable events/results/decisions, recurring themes, and his mood \
+and arc across the month. Third person, referring to him as "Brian". 5-10 \
+sentences. This is a memory record, not a reply. No preamble."""
+
+_MERGE_PROMPT = """Merge these partial monthly digests (same month) into one \
+coherent digest about Brian for that month. Keep it tight, 5-10 sentences, no \
+repetition. Third person."""
+
+
+def _batch_texts(texts: list[str], budget: int) -> list[str]:
+    blocks, buf, size = [], [], 0
+    for t in texts:
+        if size + len(t) > budget and buf:
+            blocks.append("\n\n".join(buf))
+            buf, size = [], 0
+        buf.append(t)
+        size += len(t)
+    if buf:
+        blocks.append("\n\n".join(buf))
+    return blocks
+
+
+def _call(prompt: str, body: str, backend: Backend) -> str:
+    messages: list[Message] = [
+        {"role": "system", "content": prompt},
+        {"role": "user", "content": body},
+    ]
+    return llm.complete(messages, backend=backend)
+
+
+def _digest_month(gists: list[str], backend: Backend) -> str:
+    """Map-reduce a month's session gists into one digest."""
+    blocks = _batch_texts(gists, BATCH_CHARS)
+    partials = [_call(_PROMPT, b, backend) for b in blocks]
+    while len(partials) > 1:
+        partials = [_call(_MERGE_PROMPT, g, backend) for g in _batch_texts(partials, BATCH_CHARS)]
+    return partials[0]
+
+
+def rebuild_eras(backend: Backend | None = None) -> dict:
+    """(Re)build a digest for every month that has session gists."""
+    backend = backend or config.load().summary_backend
+    by_month = memory.summaries_by_month()
+    months = 0
+    for month in sorted(by_month):
+        digest = _digest_month(by_month[month], backend)
+        memory.store_era(month, digest, len(by_month[month]))
+        months += 1
+        logbus.log("info", "era built", month=month, sessions=len(by_month[month]))
+    report = {"months": months}
+    logbus.log("info", "eras complete", **report)
+    return report
+
+
+def main() -> int:
+    report = rebuild_eras()
+    if not report["months"]:
+        print("No summaries yet — run lyra-summarize first.")
+        return 1
+    for era in memory.list_eras():
+        print(f"\n## {era.month}  ({era.session_count} sessions)\n{era.content}")
+    return 0
+
+
+if __name__ == "__main__":
+    raise SystemExit(main())