feat: persist agent report on read result records (task 0032)

Retain the agent's final report on the benchmark result record for read
tasks, so a failed read is diagnosable directly from the stored record
instead of only carrying an opaque `incorrect` tag. The runner resolves
the scoring spec once and records `run.finalReport` when the spec is a
read; mutation records omit the field entirely. The sample store needs no
change — it serializes whatever record it is handed.

This is the prerequisite for confirming the read-open-issue-count failure
from real report text before the state-aware count-line change (task 0033).

.claude/tasks/0032-bench-read-report-persistence.md

@@ -0,0 +1,26 @@
+---
+spec: read-tier-accuracy
+---
+
+## What to build
+
+Persist the agent's final report on the benchmark result record for read tasks, so a failed read is diagnosable directly from the stored record instead of only carrying an opaque `incorrect` tag.
+
+The report is already in hand where the runner scores a read task — threading it into the assembled record is all that is required; the sample store serializes whatever record it is handed and needs no change of its own.
+
+Mutation tasks are scored by diffing repository state and have no agent report, so the field is populated for read tasks and absent otherwise.
+
+## Acceptance criteria
+
+- [x] The result record carries the agent's final report for read tasks.
+- [x] The field is absent on records for mutation tasks.
+- [x] A completed read cell produces a record whose report is the agent's final report; a mutation cell produces a record without one — asserted at the runner's record-assembly seam.
+- [x] The sample store round-trips the report-bearing record without any change to the store itself.
+- [x] Existing runner and store tests still pass.
+
+## Implementation Notes
+
+- `ResultRecord` gained an optional `report?: string`. The runner resolves the scoring spec once in `runCell` and records `run.finalReport` only when `spec.kind === "read"`, so the field is populated for read tasks and absent otherwise. `makeRecord` conditionally spreads the key (`...(report !== undefined ? { report } : {})`) so a mutation (or hung) record genuinely omits it rather than carrying `report: undefined`; verified by `expect(sample).not.toHaveProperty("report")` after the JSON round-trip.
+- `scoreRun` was refactored to take a pre-resolved `ScoringSpec` instead of a `BenchTask`. This is marginally more than "thread the value into the record," but it is the minimal clean way to branch on `spec.kind` in `runCell` without calling `task.scoringSpec(owner)` twice.
+- The store needed no change, as the spec predicted: it serializes whatever record it is handed, so the round-trip test passed on first run.
+- Two review findings were left as deliberate judgement calls (both non-blocking baseline smells, no documented-standard breach): the `makeRecord` positional parameter list (extended by one param in the module's pre-existing positional style, kept consistent with surrounding code rather than refactored to an options object), and the two `spec.kind` branches a few lines apart in `runCell` and `scoreRun` (they select different things — the report vs. the scorer — and read clearer inline).