docs(engine): document the Rent-a-Loop pipeline modules

packages/loopover-engine/README.md

@@ -749,6 +749,92 @@ That resolver reads only the operator's local policy and otherwise uses safe def
 fetch a target repo's checked-in AMS policy, because untrusted repo content must not loosen operator-side budget,
 turn, slop, or submission controls. See `.loopover-ams.yml.example`.
 
+## Rent-a-Loop pipeline
+
+The customer-facing spine of Rent-a-Loop (epic #4778) is three pure, side-effect-free modules — idea → running
+loop → delivered result. Like the rest of this package they do no IO, network, wall-clock, or random reads: each
+is a deterministic transform of already-computed inputs.
+
+### `idea-intake.ts` — idea → scored, claimable task-graph
+
+Turns a freeform renter idea into a strict task-graph and dispositions it against the shared feasibility gate.
+`validateIdeaSubmission(raw)` returns a discriminated `IdeaValidationResult` (`{ ok: true, idea }` or
+`{ ok: false, errors }`), length-capping the freeform text (`IDEA_TITLE_MAX_CHARS` / `IDEA_BODY_MAX_CHARS` /
+`IDEA_CONSTRAINT_MAX_CHARS`). `buildTaskGraph(idea, drafts?)` decomposes an accepted `IdeaSubmission` into a
+`TaskGraph` of `ConstituentIssue`s (`gittensor:priority` is never emitted — it is maintainer-propagated only).
+`scoreTaskGraph(graph)` runs the feasibility gate over every issue (`TaskGraphScore`), and `buildClaimPlan(graph,
+targetRepo)` routes the scored graph into a `ClaimPlan` — `go` → `claimable`, `raise` → `deferred`, `avoid` →
+`skipped` — in dependency-respecting order.
+
+```ts
+import { validateIdeaSubmission, buildTaskGraph, scoreTaskGraph, buildClaimPlan } from "@loopover/engine";
+
+const result = validateIdeaSubmission({
+  id: "idea-1",
+  title: "Add CSV export to the reports page",
+  body: "Users want to download the reports table as CSV so they can pivot it in a spreadsheet.",
+  targetRepo: "acme/reports",
+  priority: "high",
+});
+if (result.ok) {
+  const graph = buildTaskGraph(result.idea);
+  scoreTaskGraph(graph); // { verdict: "go", perIssue: [{ key: "issue-1", verdict: "go", reasons: [] }] }
+  buildClaimPlan(graph, "acme/reports");
+  // { ideaId: "idea-1", targetRepo: "acme/reports", graphVerdict: "go",
+  //   claimable: [{ key: "issue-1", title: "Add CSV export to the reports page", targetRepo: "acme/reports", verdict: "go", reasons: [] }],
+  //   deferred: [], skipped: [] }
+}
+```
+
+### `loop-progress.ts` — running loop → customer progress snapshot
+
+`buildProgressSnapshot(state)` turns already-computed `LoopProgressState` into a `ProgressSnapshot` — the
+`LoopPhase` (`queued` → … → `done`), `LoopRunStatus`, iteration budget as `percentComplete` (or `null` when the
+budget is unknown), a `recentActivity` tail capped at `MAX_PROGRESS_ACTIVITY`, and a `done` flag. `progressChanged(prev,
+next)` decides when a snapshot changed enough to push, so the surface streams on change instead of polling (a `null`
+`prev` — the first snapshot — always pushes).
+
+```ts
+import { buildProgressSnapshot, progressChanged } from "@loopover/engine";
+
+const snapshot = buildProgressSnapshot({
+  iteration: 2,
+  maxIterations: 5,
+  phase: "coding",
+  status: "running",
+  recentActivity: [{ step: "claiming" }, { step: "coding", detail: "editing reports.tsx" }],
+});
+// { phase: "coding", status: "running", iteration: 2, maxIterations: 5, percentComplete: 40,
+//   recentActivity: [{ step: "claiming" }, { step: "coding", detail: "editing reports.tsx" }], done: false }
+progressChanged(null, snapshot); // true (first snapshot always pushes)
+```
+
+### `results-payload.ts` — completed iteration → customer result
+
+`buildResultsPayload(result)` packages a finished `IterationResult` into a customer-facing `ResultsPayload`: the
+canonical `prLink` (or `null` when no PR was opened), one plain-language `summary` sentence, a `diffPreview` bounded
+to `MAX_DIFF_PREVIEW_FILES` files (while `totals` still reflects the full change), and the `totals` roll-up. It
+formats already-fetched metadata only — it does not open, fetch, or deliver anything.
+
+```ts
+import { buildResultsPayload } from "@loopover/engine";
+
+buildResultsPayload({
+  repoFullName: "acme/reports",
+  prNumber: 128,
+  title: "Add CSV export",
+  changedFiles: [
+    { path: "src/reports.tsx", additions: 40, deletions: 3 },
+    { path: "src/csv.ts", additions: 22, deletions: 0 },
+  ],
+  status: "open",
+});
+// { prLink: "https://github.com/acme/reports/pull/128",
+//   summary: "Opened PR #128 in acme/reports: Add CSV export. 2 files changed (+62 / -3). Status: open.",
+//   diffPreview: [{ path: "src/reports.tsx", additions: 40, deletions: 3 }, { path: "src/csv.ts", additions: 22, deletions: 0 }],
+//   totals: { files: 2, additions: 62, deletions: 3 } }
+```
+
 ## Repo map builder
 
 `buildRepoMap(files)` gives a coding-agent driver (or the acceptance-criteria/prompt-packet builders upstream of