agents: self-contained agent files with embedded prompts

Each agent is a .agent file: JSON config on the first line, blank line,
then the raw prompt markdown. Fully self-contained, fully readable.
No separate template files needed.

Agents dir: checked into repo at poc-memory/agents/. Code looks there
first (via CARGO_MANIFEST_DIR), falls back to ~/.claude/memory/agents/.

Three agents migrated: replay, linker, transfer.

Co-Authored-By: ProofOfConcept <poc@bcachefs.org>

poc-memory/src/agents/prompts.rs

@@ -30,7 +30,12 @@ pub fn load_prompt(name: &str, replacements: &[(&str, &str)]) -> Result<String,
     Ok(content)
 }
 
-/// Format topology header for agent prompts — current graph health metrics
+/// Format topology header for agent prompts — current graph health metrics.
+/// Public alias for use from defs.rs (config-driven agents).
+pub fn format_topology_header_pub(graph: &Graph) -> String {
+    format_topology_header(graph)
+}
+
 fn format_topology_header(graph: &Graph) -> String {
     let sigma = graph.small_world_sigma();
     let alpha = graph.degree_power_law_exponent();
@@ -74,6 +79,11 @@ fn format_topology_header(graph: &Graph) -> String {
         n, e, graph.community_count(), sigma, alpha, gini, avg_cc, hub_list)
 }
 
+/// Public alias for use from defs.rs (config-driven agents).
+pub fn format_nodes_section_pub(store: &Store, items: &[ReplayItem], graph: &Graph) -> String {
+    format_nodes_section(store, items, graph)
+}
+
 /// Format node data section for prompt templates
 fn format_nodes_section(store: &Store, items: &[ReplayItem], graph: &Graph) -> String {
     let hub_thresh = graph.hub_threshold();
@@ -444,6 +454,11 @@ pub fn consolidation_batch(store: &Store, count: usize, auto: bool) -> Result<()
 /// Returns an AgentBatch with the prompt text and the keys of nodes
 /// selected for processing (for visit tracking on success).
 pub fn agent_prompt(store: &Store, agent: &str, count: usize) -> Result<AgentBatch, String> {
+    // Config-driven agents take priority over hardcoded ones
+    if let Some(def) = super::defs::get_def(agent) {
+        return super::defs::run_agent(store, &def, count);
+    }
+
     let graph = store.build_graph();
     let topology = format_topology_header(&graph);