capture: name the render source in the exact-bounds refusal, and put its one-frame tolerance under test

The tolerance is unchanged and now derived, not assumed: frameCountFor lands in {floor(L), ceil(L)}, so a non-frame-aligned window can never miss by more than a frame. Naming the source is what tells a self-bounding render from a short one.

docs/VERIFICATION.md

@@ -26,6 +26,8 @@ Checks for Θ, Ξ, and Ψ work that no unit test can close. Build **Release**, i
 - [ ] Same source: track scope × time selection, and track scope × razor — same exact window (`PLAN.md:2136`)
 - [ ] One razor-union case (two disjoint areas, one track) — lands the requested window, no `ReaSampler capture failed:` line (`PLAN.md:2137`)
 - [ ] Capture an item whose extent already equals the window — still lands, unchanged (the byte-identity regression floor) (`docs/COMPLETED.md:829`)
+- [ ] **Open blocker.** A live capture refused with a 38-frame shortfall (195216 of 195254 at 48 kHz). Set View → time unit to Samples, then over the same range run **track** scope and **item** scope in turn and report the refusal's `Render source:` line plus both frame counts, and whether the media under the range ends before the range does
+- [ ] Same range extended ~1 s past all media, track scope — a full-length file with trailing silence means postprocessing is off; a short file means a trailing-silence trim is firing despite `RENDER_NORMALIZE &(4<<16)`
 
 ## Names and channels