docs: flat UDP spec and plan amendment -- vector rows as channels or as a waveform

docs/superpowers/specs/2026-11-02-flat-udp-source-design.md

@@ -120,3 +120,28 @@ README (the kind and its limits: no loss detection, the signal list is the user'
 responsibility), `docs/claude/build-and-run.md` (options and mock usage),
 `docs/claude/architecture.md` (source plugins), `docs/claude/probe-readings.md` and
 `docs/claude/verification.md` (the new probe lines).
+
+## Amendment 2026-11-02: how a vector signal is shown (decided with the user during Task 2)
+
+Task 2 found that treating every vector row as one channel of `count` consecutive samples zero-pads
+the scalar channels of a mixed list (the model spans a frame by its largest element block, and
+`Frame::value` is 0 past a scalar's one value) and declares the wrong rate for the vector channel.
+Both readings of a vector are useful depending on the sender, so each vector row picks one:
+
+- **`channels` (default).** `Wave:float32[16]` becomes 16 scalar channels named `Wave[0]` .. `Wave[15]`,
+  one sample per cycle each. All such lists are batched like an all-scalar list.
+- **`waveform`.** `Wave:float32[16]w` is ONE channel receiving a block of `count` consecutive samples per
+  cycle: `SignalInfo{rows=count, cols=1, sampling_rate=rate*count}`, one datagram per `Frame`
+  (`num_samples = 1`).
+
+Rules:
+- The `signals` string takes an optional trailing `w` after the count; `format` emits it only for a waveform row.
+- A waveform row needs `count > 1`.
+- A list with a waveform row must contain only waveform rows, all with the same `count`; otherwise it is
+  invalid, with a message the form shows. (No zero-padding, no holding scalars across a block.)
+- The channel total is capped at 256: scalars count 1, a `channels` row counts `count`, a waveform row counts 1.
+  Over the cap is invalid.
+- `block` batching applies whenever the list has no waveform row; with a waveform row it is 1.
+- The form shows a "Vector as" dropdown (`Channels` / `Waveform`) on rows whose count is above 1, and
+  the channel total in the subtitle.
+- The earlier "Data flow" text saying every vector row forces `num_samples = 1` applies to waveform rows only.