learnings: audit fixes — preamble in TOC, server-side line-boundary truncation, empty-repo intro (#743)

* learnings: surface preamble in TOC, mirror line-boundary truncation server-side, fix empty-repo intro copy

three audit fixes on top of the recent learnings overhaul (#717):

- `parseLearningsHeadings` now prepends a synthetic `(preamble)` entry
  when a body has non-whitespace content before the first heading. the
  prompt instructs the agent NOT to slurp the whole file when a TOC is
  present, so without this any preamble lines were silently invisible
  (realistic transitional case: an agent partially restructures a
  legacy free-text body and leaves bullets above the first `## `).

- server-side PATCH route now applies the same line-boundary-aware
  truncation as the action (defense in depth via a shared
  `truncateAtLineBoundary` + `MAX_LEARNINGS_LENGTH` exported from
  `action/internal`). the raw `.slice` it used before could leave a
  mid-heading tail on any caller that bypassed the client-side
  truncate, breaking the next-seed TOC parse. removes the duplicated
  cap constant.

- `buildLearningsSection` intro no longer asserts "accumulated by
  previous agent runs" — false for fresh repos with zero history. new
  copy is tense-neutral and works for empty + populated bodies. also
  nudges the agent to re-read after mid-run edits (the inlined TOC
  ranges are a run-start snapshot).

Co-authored-by: Cursor <cursoragent@cursor.com>

* learnings prompt: tighten to single evergreen test, allow tool-quirk bullets when they prevent repeat waste

The blanket "no pullfrog tool quirks" ban was wrong — if the agent burned
calls discovering a quirk this run, recording the workaround prevents the
next run from repeating the waste. Reframe around one litmus ("would a
future run do its work better because this bullet exists?") and trust it
to subsume the scattered don'ts. Drop the 3+ months timeframe (arbitrary)
and the four-example pullfrog/PR/date/play-by-play list (the rule
underneath is "don't anchor facts to repo state that will move"). Cuts
~10 lines from a prompt the model was already mostly ignoring; the
remaining anchor list is narrower and more enforceable.

* audit-learnings-r2: align wiki + tighten re-read nudge

- wiki/prompt.md described the post-run reflection prompt as "bans pullfrog-tool quirks (those belong in tool descriptions, not per-repo learnings), bans PR/review/commit/date references" — that's stale after the prompt rewrite. update to: single-litmus framing, expanded anchor list (now includes version pins + line numbers), and explicit allowance for tool-quirk workarounds when discovery burned calls.
- buildLearningsSection re-read nudge said "re-read after editing" which can be read as "re-read the section you edited". in fact any edit shifts the line numbers of every later section in the TOC, not just the edited one. tighten to make that explicit. mirror the new wording in the wiki example block. update the test substring assertion accordingly.

* postRun: refresh JSDoc to match the reflection prompt rewrite

`buildLearningsReflectionPrompt`'s JSDoc still listed "PR-/review-/commit-/date-anchored facts" and "rediscovery of pullfrog-tool quirks" as failure modes the prompt pushes back on. after b586b4f8 the prompt no longer bans tool-quirk bullets (it explicitly allows them when the agent burned calls discovering the quirk), and the anchor list expanded to cover branch refs, version pins, and line numbers too. update the JSDoc so it describes the prompt that actually exists, and call out the cross-repo drift tradeoff that comes with allowing tool-quirk bullets.

* fix(mcp/issueEvents): narrow event.event before Set.has lookup

octokit's listEventsForTimeline union includes timeline-event members where `event` is `event?: string`. `("event" in event)` does not narrow that property to non-undefined, so `relevantEventTypes.has(event.event)` was passing `string | undefined` to a `Set<string>.has`. typescript only flagged this once `cf-worker-indexing` started seeing the file via the type graph that now reaches mcp through the new `truncateAtLineBoundary` re-export in `action/internal/index.ts`. fix the latent bug at the source: require `typeof event.event === "string"` before the Set lookup.

* learnings: split truncation helpers into MCP-free module

re-exporting `truncateAtLineBoundary` + `MAX_LEARNINGS_LENGTH` from `action/utils/learnings.ts` through `action/internal/index.ts` accidentally pulled the entire MCP type graph into the SDK barrel: `learnings.ts` imports `ToolContext` from `mcp/server.ts`, which transitively wires every tool module under `action/mcp/` into anything that imports from `pullfrog/internal`. for `cf-worker-indexing/tsconfig.json` (`customConditions: ["@pullfrog/source"]`) and the root `tsc` (which compiles the proprietary app routes that import from `pullfrog/internal`), this expanded the type-checked surface and surfaced two latent issues in unrelated files (`mcp/issueEvents.ts`, `utils/subprocess.ts`). a 6-line pure string helper has no business dragging mcp/server.ts into anyone else's type graph.

move both symbols to `action/utils/learningsTruncate.ts`. `learnings.ts` re-exports them so existing callers keep working; `internal/index.ts` re-exports from the truncate-only module so the SDK barrel stays MCP-free.

---------

Co-authored-by: Cursor <cursoragent@cursor.com>
Co-authored-by: Colin McDonnell <colinmcd94@gmail.com>

agents/postRun.ts

@@ -279,11 +279,18 @@ export function shouldRunReflection(mode: string | undefined): boolean {
  * agent has been writing (issue #619 in pullfrog/app). recurring failure
  * modes the framing pushes back on:
  *  - massive multi-paragraph "bullets" that are really mini-articles
- *  - PR-/review-/commit-/date-anchored facts that decay within weeks
- *  - rediscovery of pullfrog-tool quirks that belong in tool descriptions,
- *    not per-repo learnings
+ *  - facts anchored to moving repo state (PR / review / commit / branch
+ *    refs, dates, version pins, line numbers) that decay within weeks
  *  - sections growing into giant flat lists with no internal structure,
  *    forcing future runs to read kilobytes to find one fact
+ *
+ * single litmus delivered in the prompt: "would a future run on this repo
+ * do its work better because this bullet exists?". tool-quirk workarounds
+ * are explicitly allowed when the agent burned calls discovering the
+ * quirk this run — recording the workaround prevents next run from
+ * repeating the waste. tradeoff: the same quirk gets duplicated across
+ * repos, so when a quirk is fixed upstream in tool descriptions the
+ * per-repo bullets go stale and we have no batch-invalidation path.
  */
 export function buildLearningsReflectionPrompt(filePath: string): string {
   return [
@@ -296,18 +303,16 @@ export function buildLearningsReflectionPrompt(filePath: string): string {
     `- **no section over ~300 lines.** when a section is approaching that, split it: introduce \`### \` subsections grouping related bullets, or hoist a coherent group into a new top-level \`## \` section. granular sections mean future runs read targeted line ranges instead of slurping the whole file. this is the most important hygiene rule on long-lived repos.`,
     `- if you find a flat unstructured list (legacy content from before this format), restructure it: read it, group related bullets, rewrite the file with \`## \` / \`### \` headings around them. don't preserve bad structure — fix it.`,
     "",
-    `bullet hygiene:`,
-    `- one fact per line starting with \`- \`. each bullet is ONE specific durable fact, not a paragraph or essay.`,
-    `- aim for ≤ 240 chars per bullet. longer bullets are almost always mixing multiple facts that should be split, or burying the durable claim under PR-specific context that should be cut.`,
-    `- only add bullets when the finding is high-confidence AND broadly useful AND will still be true in 3+ months. skip speculative, one-off, or "maybe" findings.`,
-    `- prune bullets that are clearly wrong, no longer relevant, or low-signal. a focused, accurate file beats a long stale one. compressing two overlapping bullets into one tighter bullet counts as progress.`,
-    `- deduplicate against existing entries (in any section) — if a bullet covers the same fact, update it in place instead of adding a duplicate.`,
+    `the only test: would a future run on this repo do its work better because this bullet exists? useful for future runs in this repo — prevent wasted tool calls, rabbit holes, and mistakes.`,
     "",
-    `do NOT add bullets for:`,
-    `- pullfrog tool quirks (e.g. "\`shell\` timeout is in milliseconds", "\`git\` args must be a JSON array", "\`create_pull_request_review\` drops out-of-hunk comments", "\`push_branch\` may report timeout when push succeeded"). these are universal across repos and belong in the tool descriptions — flag the gap rather than hoarding the workaround per-repo.`,
-    `- references to specific PR numbers, review IDs, commit SHAs, branch names, or person handles ("PR #595 introduced X", "flagged in review 12345", "as of commit abc123"). repo state changes; these decay into noise within weeks.`,
-    `- dated assertions ("as of May 2026", "currently...", "for now..."). if a fact needs a date to be true, it isn't durable enough to belong here.`,
-    `- play-by-play of what THIS run did. learnings are for the NEXT run, not a retrospective.`,
+    `bullet hygiene:`,
+    `- one fact per line starting with \`- \`, ≤ 240 chars.`,
+    `- only add when high-confidence, broadly useful, evergreen.`,
+    `- prune wrong or low-signal bullets; merge overlaps; dedupe across sections.`,
+    "",
+    `don't anchor facts to repo state that will move: PR / review / commit / branch refs, dates, version pins, line numbers. state the rule directly. if it needs the anchor to be load-bearing, it isn't evergreen.`,
+    "",
+    `tool-quirk bullets are fine when you burned calls discovering the quirk and a future run would repeat them. write the workaround, not the war story.`,
     "",
     `if you have nothing substantively new to add AND the existing entries still look healthy and well-structured, leave the file alone — just reply "done" and stop. silence is a valid outcome.`,
   ].join("\n");