Scope candidate blob readers to validation

docs/roadmap/implementation.md

@@ -1,6 +1,6 @@
 # Computational Efficiency Implementation Plan
 
-**Status:** Stages 1–4 complete; Stages 5–11 pending.
+**Status:** Stages 1–5 complete; Stages 6–11 pending.
 
 ## Purpose And Baseline
 
@@ -316,6 +316,22 @@ preserve workspace/file-size metadata behavior. Re-run content benchmarks with
 reader startup and closure included in the content-operation timing. Update
 [validation mechanics](../internal/validation.md) for the landed lifecycle.
 
+**Completion:** Complete. `CandidateTree` owns a lazy batch reader and exposes
+idempotent cleanup. The shared executor closes it on every post-load return,
+before product checks or build callbacks; metadata-only runs leave it unstarted.
+Earlier check failures and cancellation remain primary, while an unexpected
+reader exit after successful content checks becomes a contextual failure for
+the last content-reading check. Direct tree users close their readers. The
+temporary object-ID byte cache remains until Stage 6. Validation, candidate,
+and root facade tests passed. Content benchmark timings now include reader
+startup and close (Go 1.26.8, Git 2.53.0, Linux x86_64 Intel Core i5-7260U,
+three repetitions): unique reads took 59.8–77.9 ms loose and 22.8–43.0 ms
+packed; unique-file formatting took 114–188 ms loose and 33.7–55.7 ms packed;
+repeated-ID reads took 2.18–6.45 ms, repeated-ID formatting took 4.75–6.62 ms,
+and the Markdown workload took 15.0–16.9 ms. Compared with the Stage 1 timings,
+these measurements reflect the shared Git process and include its lifecycle;
+timing varies on the shared machine.
+
 ## Stage 6: Release One-Use Source Bytes And Reuse Formatting Results
 
 **Owners:** `internal/validation/tree.go`, `validation.go`, and destination tests.