learnings: edit-in-place tmpfile (drop update_learnings tool) (#635)

* learnings: edit-in-place tmpfile (drop update_learnings tool)

learnings now follow the PR-summary file pattern: server seeds
`pullfrog-learnings.md` from `Repo.learnings` at startup, agent reads
it as part of context, may edit in place during the post-run reflection
turn, server reads back at end-of-run and PATCHes if changed.

motivation: `update_learnings` required the agent to pass the FULL
merged list as a string parameter — an output-token tax that grew
linearly with the learnings size, and a constant prompt-context
expansion since the contents were also inlined into the LEARNINGS
section. for repos with mature learnings the prompt was getting
visibly noisy in CI logs.

key changes:
- new `action/utils/learnings.ts` (seed/read helpers + 10k cap)
- `main.ts`: always seed; `persistLearnings` mirrors `persistSummary`
  (success path, error path, exit-signal handler, idempotent guard,
  byte-trim equality skip); forwards `model` for `LearningsRevision.model`
- `LEARNINGS` prompt section now contains only the file path + a
  one-line "read it" instruction (no contents inlined)
- `update_learnings` MCP tool deleted; `action/mcp/learnings.ts` removed
- reflection turn (`buildLearningsReflectionPrompt`) reframed around
  file editing with explicit prune-stale + leave-alone-if-nothing-new
  framing
- `learningsStep` removed from every mode checklist — surface lives only
  in the LEARNINGS prompt section + the reflection turn now

* learnings: harden seed step + refresh stale docs (review feedback)

Three findings from PR review, all implemented:

1. wrap learnings seed in best-effort try/catch (action/main.ts) —
   the always-on seed block ran unconditionally and an unwrapped
   `seedLearningsFile` (mkdir + writeFile) failure (ENOSPC, EACCES,
   hostile sandbox) would unwind into the outer main() catch and flip
   an otherwise-successful run to "❌ Pullfrog failed" before the
   agent even started. asymmetric with `persistLearnings`'s own
   best-effort contract. wrap and log on failure; downstream
   consumers (`persistLearnings`, agent harnesses, `resolveInstructions`)
   already handle `learningsFilePath: undefined` cleanly.

2. refresh wiki/main.md — `resolveInstructions` parameter renamed
   from `learnings` to `learningsFilePath` in this PR; the data-flow
   diagram and the resolver dependency table both still showed the
   pre-refactor signature.

3. drop deleted `learnings.ts` from ROADMAP.md + RESEARCH.md
   "missing MCP tool tests" bullets — `action/mcp/learnings.ts` was
   removed in this PR; the bullets are otherwise still accurate.

agents/postRun.test.ts

@@ -42,10 +42,10 @@ describe("runPostRunRetryLoop — reflection turn", () => {
   });
 
   it("does not flip a successful run to failed when reflection returns success:false", async () => {
-    // the reflection turn is a best-effort nudge (update_learnings). if it
-    // fails — e.g. the model API errors mid-turn — the underlying task has
-    // already completed and been gated cleanly, so the run as a whole must
-    // still be reported as successful.
+    // the reflection turn is a best-effort nudge (edit the learnings
+    // tmpfile). if it fails — e.g. the model API errors mid-turn — the
+    // underlying task has already completed and been gated cleanly, so the
+    // run as a whole must still be reported as successful.
     const initial = successResult({ output: "task done" });
     const resume = vi
       .fn<(ctx: { prompt: string; previousResult: AgentResult }) => Promise<AgentResult>>()
@@ -56,7 +56,7 @@ describe("runPostRunRetryLoop — reflection turn", () => {
       initialUsage: undefined,
       stopScript: null,
       resume,
-      reflectionPrompt: "REFLECTION: call update_learnings if anything is worth saving",
+      reflectionPrompt: "REFLECTION: edit learnings file if anything is worth saving",
     });
 
     expect(result.success).toBe(true);
@@ -110,7 +110,7 @@ describe("runPostRunRetryLoop — reflection turn", () => {
       initialUsage: undefined,
       stopScript: null,
       resume,
-      reflectionPrompt: "REFLECTION: consider update_learnings",
+      reflectionPrompt: "REFLECTION: consider editing learnings",
     });
 
     expect(result.success).toBe(true);
@@ -135,7 +135,7 @@ describe("runPostRunRetryLoop — reflection turn", () => {
       initialUsage: undefined,
       stopScript: null,
       resume,
-      reflectionPrompt: "REFLECTION: consider update_learnings",
+      reflectionPrompt: "REFLECTION: consider editing learnings",
     });
 
     expect(result.success).toBe(true);
@@ -186,7 +186,7 @@ describe("runPostRunRetryLoop — reflection turn", () => {
       initialUsage: undefined,
       stopScript: null,
       resume,
-      reflectionPrompt: "REFLECTION: consider update_learnings",
+      reflectionPrompt: "REFLECTION: consider editing learnings",
     });
 
     expect(result.success).toBe(true);