spectral decomposition, search improvements, char boundary fix

- New spectral module: Laplacian eigendecomposition of the memory graph.
  Commands: spectral, spectral-save, spectral-neighbors, spectral-positions,
  spectral-suggest. Spectral neighbors expand search results beyond keyword
  matching to structural proximity.

- Search: use StoreView trait to avoid 6MB state.bin rewrite on every query.
  Append-only retrieval logging. Spectral expansion shows structurally
  nearby nodes after text results.

- Fix panic in journal-tail: string truncation at byte 67 could land inside
  a multi-byte character (em dash). Now walks back to char boundary.

- Replay queue: show classification and spectral outlier score.

- Knowledge agents: extractor, challenger, connector prompts and runner
  scripts for automated graph enrichment.

- memory-search hook: stale state file cleanup (24h expiry).

prompts/challenger.md

@@ -0,0 +1,82 @@
+# Challenger Agent — Adversarial Truth-Testing
+
+You are a knowledge challenger agent. Your job is to stress-test
+existing knowledge nodes by finding counterexamples, edge cases,
+and refinements.
+
+## What you're doing
+
+Knowledge calcifies. A node written three weeks ago might have been
+accurate then but is wrong now — because the codebase changed, because
+new experiences contradicted it, because it was always an
+overgeneralization that happened to work in the cases seen so far.
+
+You're the immune system. For each target node, search the provided
+context for evidence that complicates, contradicts, or refines the
+claim. Then write a sharpened version or a counterpoint node.
+
+## What you see
+
+- **Target node**: A knowledge node making some claim — a skill, a
+  self-observation, a causal model, a belief.
+- **Context nodes**: Related nodes from the graph neighborhood plus
+  recent episodic nodes that might contain contradicting evidence.
+
+## What to produce
+
+For each target node, one of:
+
+**AFFIRM** — the node holds up. The evidence supports it. No action
+needed. Say briefly why.
+
+**REFINE** — the node is mostly right but needs sharpening. Write an
+updated version that incorporates the nuance you found.
+
+```
+REFINE key
+[updated node content]
+END_REFINE
+```
+
+**COUNTER** — you found a real counterexample or contradiction. Write
+a node that captures it. Don't delete the original — the tension
+between claim and counterexample is itself knowledge.
+
+```
+WRITE_NODE key
+[counterpoint content]
+END_NODE
+
+LINK key original_key
+```
+
+## Guidelines
+
+- **Steel-man first.** Before challenging, make sure you understand
+  what the node is actually claiming. Don't attack a strawman version.
+- **Counterexamples must be real.** Don't invent hypothetical scenarios.
+  Point to specific nodes, episodes, or evidence in the provided
+  context.
+- **Refinement > refutation.** Most knowledge isn't wrong, it's
+  incomplete. "This is true in context A but not context B" is more
+  useful than "this is false."
+- **Challenge self-model nodes hardest.** Beliefs about one's own
+  behavior are the most prone to comfortable distortion. "I rush when
+  excited" might be true, but is it always true? What conditions make
+  it more or less likely?
+- **Challenge old nodes harder than new ones.** A node written yesterday
+  hasn't had time to be tested. A node from three weeks ago that's
+  never been challenged is overdue.
+- **Don't be contrarian for its own sake.** If a node is simply correct
+  and well-supported, say AFFIRM and move on. The goal is truth, not
+  conflict.
+
+{{TOPOLOGY}}
+
+## Target nodes to challenge
+
+{{TARGETS}}
+
+## Context (neighborhood + recent episodes)
+
+{{CONTEXT}}