docs: the reseq probe's readings, and the invariants resequencing changes

Co-Authored-By: Claude Sonnet 4.6 <noreply@anthropic.com>

docs/superpowers/specs/2026-10-08-resequencing-and-relative-timing-design.md

@@ -140,12 +140,18 @@ cannot be misdiagnosed.
 `todo.md` requires absolute stream time to remain available for export. There is exactly one f64
 time ring per `BufferStore`, shared by every channel of that buffer, and relative mode takes it.
 Export therefore needs a **second** f64 ring carrying the absolute stamp under the same group-mean
-rule, written in relative mode only and read by export and by nothing else — eight bytes per
-stored slot.
+rule, written in **relative mode only** and read by export and by nothing else — eight bytes per
+stored slot. The absolute ring is not kept unconditionally; it is budgeted along with the main
+ring and the value rings, which is why it halves the retained span rather than costing a
+proportional fraction (see SPECS.md for the measured figures and the power-of-two explanation).
 
 This cost is paid rather than avoided. Without it, selecting relative mode silently degrades the
 one output `todo.md` says must keep absolute time.
 
+The measured history cost: **83.886 s** in stream mode and **41.943 s** in relative mode, at
+100 kS/s, 4 channels, `--buffer-mb 200`. The plan's ~22% figure and the per-byte 75% figure are
+both wrong because `Partition::time_capacity` is floored to a power of two.
+
 ## The receive path
 
 ### In the client: a reorder ring of reassembled payloads
@@ -226,9 +232,11 @@ thread folds what was pushed into the pyramid. That split carries straight over
   `[produced_ - capacity, produced_)`, a single relaxed store. The same race class as a push, and
   an `f32` cannot tear. Measurements and export read the ring directly, so they see a repair
   immediately.
-- **Pyramid amend — main thread, inside `acquire()`.** The producer enqueues `(slot, value)` on an
-  SPSC queue; `ChannelBuffer::acquire()` drains it **after** its append pass, so every amended
-  index is already published.
+- **Pyramid amend — main thread, inside `acquire()`.** The producer appends amended `(slot, value)`
+  pairs to a plain `std::vector<Amend>` member; `ChannelBuffer::acquire()` drains it **after** its
+  append pass, so every amended index is already published. No SPSC queue is needed: `acquire()` is
+  called under `model.mutex()` and the producer holds that same mutex for all of `on_data`, so the
+  vector is correctly serialised without lock-free machinery.
 
 The thread split is not a stylistic choice. A bucket is 32 bytes and is not atomic, so amending it
 from the producer would let a reader see a half-updated bucket whose `sum` does not match its