provenance: track agent phase, use task_local + thread_local

Split TASK_PROVENANCE into TASK_AGENT (task_local, set once per agent
run) and TASK_PHASE (thread_local, updated between steps). Provenance
now reports "agent:surface-observe:observe" instead of just
"agent:surface-observe", making it possible to identify which pipeline
phase created a node.

Priority: task_local agent + thread_local phase > POC_PROVENANCE env
var > "manual".

Also includes memory_search catchup throttle and pipelining fixes
from the surface-observe refactor.

src/subconscious/knowledge.rs

@@ -339,6 +339,11 @@ fn run_one_agent_inner(
     }
     log("\n=== CALLING LLM ===");
 
+    // Set initial phase for provenance tracking
+    if let Some(first_phase) = step_phases.first() {
+        crate::store::set_phase(first_phase);
+    }
+
     // Bail check: if the agent defines a bail script, run it between steps.
     // The script receives the pid file path as $1, cwd = state dir.
     let bail_script = def.bail.as_ref().map(|name| {
@@ -349,9 +354,10 @@ fn run_one_agent_inner(
     let state_dir_for_bail = state_dir.clone();
     let pid_path_for_bail = pid_path.clone();
     let bail_fn = move |step_idx: usize| -> Result<(), String> {
-        // Update phase
+        // Update phase in pid file and provenance tracking
         if step_idx < step_phases.len() {
             write_pid(&step_phases[step_idx]);
+            crate::store::set_phase(&step_phases[step_idx]);
         }
         // Run bail script if defined
         if let Some(ref script) = bail_script {