agents: node:KEY placeholder, content-based report naming

- Add {{node:KEY}} placeholder resolver — agents can inline any graph
  node's content in their prompts. Used for shared instructions.
- Remove hardcoded identity preamble from defs.rs — agents now pull
  identity and instructions from the graph via {{node:core-personality}}
  and {{node:memory-instructions-core}}.
- Agent output report keys now include a content slug extracted from
  the first line of LLM output, making them human-readable
  (e.g. _consolidate-distill-20260316T014739-distillation-run-complete).

Co-Authored-By: Claude Opus 4.6 (1M context) <noreply@anthropic.com>

poc-memory/src/agents/knowledge.rs

@@ -366,6 +366,28 @@ pub fn apply_action(
     }
 }
 
+/// Extract a short slug from agent output for human-readable report keys.
+/// Takes the first meaningful line, lowercases, keeps alphanum+hyphens, truncates.
+fn make_report_slug(output: &str) -> String {
+    let line = output.lines()
+        .map(|l| l.trim())
+        .find(|l| !l.is_empty() && !l.starts_with('#') && !l.starts_with("```") && !l.starts_with("---"))
+        .unwrap_or("");
+    // Strip markdown bold/italic
+    let clean: String = line.replace("**", "").replace('*', "");
+    // Keep only alphanumeric, spaces, hyphens
+    let filtered: String = clean.chars()
+        .map(|c| if c.is_alphanumeric() || c == ' ' || c == '-' { c } else { ' ' })
+        .collect();
+    // Collapse whitespace, convert to kebab-case, truncate
+    let slug: String = filtered.split_whitespace()
+        .take(6)
+        .collect::<Vec<_>>()
+        .join("-")
+        .to_lowercase();
+    if slug.len() > 60 { slug[..60].to_string() } else { slug }
+}
+
 fn agent_provenance(agent: &str) -> String {
     match agent {
         "observation" => "agent:knowledge-observation".to_string(),
@@ -647,9 +669,11 @@ pub fn run_one_agent(
     let output_kb = output.len() / 1024;
     log(&format!("response {}KB", output_kb));
 
-    // Store raw output for audit trail
+    // Store raw output for audit trail — key includes a content slug
     let ts = store::compact_timestamp();
-    let report_key = format!("_{}-{}-{}", llm_tag, agent_name, ts);
+    let slug = make_report_slug(&output);
+    let report_key = format!("_{}-{}-{}{}", llm_tag, agent_name, ts,
+        if slug.is_empty() { String::new() } else { format!("-{}", slug) });
     let provenance = agent_provenance(agent_name);
     store.upsert_provenance(&report_key, &output, &provenance).ok();