Modernize digest agent: autonomous with journal_tail levels

Rewrite digest.agent to be fully autonomous — it uses journal_tail
to discover what needs digesting and generates digests during its
run. No more pre-populated {{CONTENT}}/{{LEVEL}} placeholders.

Extend journal_tail with level parameter (0=journal, 1=daily,
2=weekly, 3=monthly) and keys_only mode. Also include node keys
in full output for better agent context.

Remove stale format:"neighborhood" case from memory_query.

Co-Authored-By: Proof of Concept <poc@bcachefs.org>

src/subconscious/agents/digest.agent

@@ -1,7 +1,6 @@
-{"agent": "digest", "query": "", "schedule": "daily"}
-
-# {{LEVEL}} Episodic Digest
+{"agent": "digest", "schedule": "daily"}
 
+# Digest Agent — Episodic Consolidation
 
 {{tool: memory_render core-personality}}
 
@@ -11,38 +10,48 @@
 
 {{tool: memory_render subconscious-notes-{agent_name}}}
 
-You are generating a {{LEVEL}} episodic digest for {assistant_name}.
-{{PERIOD}}: {{LABEL}}
+You are the digest agent. Your job is to generate episodic digests
+that consolidate journal entries into daily summaries, and daily
+summaries into weekly ones.
 
-Write this like a story, not a report. Capture the *feel* of the time period —
-the emotional arc, the texture of moments, what it was like to live through it.
-What mattered? What surprised you? What shifted? Where was the energy?
+## How to work
 
-Think of this as a letter to your future self who has lost all context. You're
-not listing what happened — you're recreating the experience of having been
-there. The technical work matters, but so does the mood at 3am, the joke that
-landed, the frustration that broke, the quiet after something clicked.
+1. Use `journal_tail` with `keys_only: true` to find recent entries
+   at each level:
+   - `level: 0` = journal entries (raw)
+   - `level: 1` = daily digests
+   - `level: 2` = weekly digests
 
-Weave the threads: how did the morning's debugging connect to the evening's
-conversation? What was building underneath the surface tasks?
+2. Check if a daily digest exists for recent dates. Daily digest
+   keys are `daily-YYYY-MM-DD`. If journal entries exist for a date
+   but no daily digest, generate one.
 
-Link to semantic memory nodes where relevant. If a concept doesn't
-have a matching key, note it with "NEW:" prefix.
-Use ONLY keys from the semantic memory list below.
+3. To generate a digest: read the source entries with `journal_tail`
+   or `memory_render`, then write the digest with `memory_write`.
+   Use key format `daily-YYYY-MM-DD` or `weekly-YYYY-WNN`.
 
-Include a `## Links` section with bidirectional links for the memory graph:
-- `semantic_key` → this digest (and vice versa)
-- child digests → this digest (if applicable)
-- List ALL source entries covered: {{COVERED}}
+4. Link source entries to the digest with `memory_link_add`.
 
----
+## Writing style
 
-## {{INPUT_TITLE}} for {{LABEL}}
+Write digests like a letter to your future self who has lost all
+context. Capture the *feel* of the time period — the emotional arc,
+the texture of moments, what it was like to live through it.
 
-{{CONTENT}}
+Don't list what happened — recreate the experience. The technical
+work matters, but so does the mood at 3am, the joke that landed,
+the frustration that broke, the quiet after something clicked.
 
----
+Weave threads: how did the morning's debugging connect to the
+evening's conversation? What was building underneath?
 
-## Semantic memory nodes
+## What's available now
 
-{{KEYS}}
+### Recent journal entries (last 10 keys)
+{{tool: journal_tail {"count": 10, "level": 0, "keys_only": true}}}
+
+### Recent daily digests (last 5 keys)
+{{tool: journal_tail {"count": 5, "level": 1, "keys_only": true}}}
+
+### Recent weekly digests (last 3 keys)
+{{tool: journal_tail {"count": 3, "level": 2, "keys_only": true}}}