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.

modes.ts

@@ -65,10 +65,6 @@ Rules:
 - Focus on *intent*, not *what* — the diff already shows what changed
 - Get the file count and commit count from the checkout_pr metadata, not by counting manually`;
 
-function learningsStep(t: (toolName: string) => string, n: number): string {
-  return `${n}. **learnings** (only if high confidence): if you discovered something about repo setup, test commands, conventions, or patterns that you are confident is correct and would reliably help future runs, call \`${t("update_learnings")}\` to persist it. skip this step if you are unsure or the finding is speculative/one-off. format as a flat bullet list (\`- \` per line, one fact per bullet). merge with existing learnings from the prompt — pass the FULL merged list. deduplicate, and drop bullets that are clearly wrong or no longer relevant to the current codebase.`;
-}
-
 export function computeModes(agentId: AgentId): Mode[] {
   const t = (toolName: string) => formatMcpToolRef(agentId, toolName);
   return [
@@ -125,8 +121,6 @@ export function computeModes(agentId: AgentId): Mode[] {
    - create a PR via \`${t("create_pull_request")}\`
    - call \`${t("report_progress")}\` with the PR link or the exact error if push/PR failed
 
-${learningsStep(t, 6)}
-
 ### Notes
 
 For simple, well-defined tasks, skip the plan phase and go straight to build.`,
@@ -155,9 +149,7 @@ For simple, well-defined tasks, skip the plan phase and go straight to build.`,
    - confirm a clean working tree, then push via \`${t("push_branch")}\` (same push/prepush guidance as Build mode in *SYSTEM*)
    - reply to each comment using \`${t("reply_to_review_comment")}\`
    - resolve addressed threads via \`${t("resolve_review_thread")}\`
-   - call \`${t("report_progress")}\` with a brief summary (or the exact push error if push failed)
-
-${learningsStep(t, 6)}`,
+   - call \`${t("report_progress")}\` with a brief summary (or the exact push error if push failed)`,
     },
     // Review and IncrementalReview use the multi-lens orchestrator pattern
     // (canonical source: .claude/commands/anneal.md). The orchestrator does
@@ -331,9 +323,7 @@ ${PR_SUMMARY_FORMAT}`,
 
 2. Produce a structured, actionable plan with clear milestones.
 
-3. Call \`${t("report_progress")}\` with the plan.
-
-${learningsStep(t, 4)}`,
+3. Call \`${t("report_progress")}\` with the plan.`,
     },
     {
       name: "Fix",
@@ -356,9 +346,7 @@ ${learningsStep(t, 4)}`,
 
 5. Finalize:
    - confirm a clean working tree, then push via \`${t("push_branch")}\` (same push/prepush guidance as Build mode in *SYSTEM*)
-   - call \`${t("report_progress")}\` with the diagnosis and fix summary (or the exact push error if push failed)
-
-${learningsStep(t, 6)}`,
+   - call \`${t("report_progress")}\` with the diagnosis and fix summary (or the exact push error if push failed)`,
     },
     {
       name: "ResolveConflicts",
@@ -403,9 +391,7 @@ ${learningsStep(t, 6)}`,
 3. Finalize:
    - if code changes were made, push to a pull request (new or existing) using \`${t("push_branch")}\` and \`${t("create_pull_request")}\` as needed. \`git status\` must be clean before you finish (see *SYSTEM* Git rules if push fails).
    - call \`${t("report_progress")}\` once with results — include exact tool errors if push or PR creation failed
-   - if the task involved labeling, commenting, or other GitHub operations, perform those directly
-
-${learningsStep(t, 4)}`,
+   - if the task involved labeling, commenting, or other GitHub operations, perform those directly`,
     },
   ];
 }