Merge branch 'card-list': the thread pane as a list of cards

Replaces the five-column grid with a single column of three-line cards. Item 53
recorded that the columns, not the cues drawn inside them, were what made the
list read as a table of records; item 20 had already shipped finished, tested
and green and been rejected on sight for exactly that reason.

A card is sender and date, subject with the flag, attachment and reply-count
marks, and tags, at one uniform height. Replies indent under a continuous spine
and show only the tags their thread does not carry. The account colour runs down
the card's left edge, replacing the chip that used to eat a third of every
subject line, with matching swatches in the account dropdown. Sorting newest or
oldest first is new and remembered.

Closes items 20, 51, 53 and 60.

The four defects that mattered were all found by rendering cards to an image and
looking at them, with the suite green through every one: a date clipped on unread
cards because bold is wider than the font the layout measured, an accent bar
painted in a colour identical to the background, an expander pill in a palette
role a theme had made equal to Base, and three separate faults from trusting
notmuch's reply depth to mean structure when it only means how notmuch happened
to thread the mail.

2 files changed, 21 insertions, 18 deletions

diff --git a/docs/superpowers/plans/2026-08-03-post-0.1.0-usability.md b/docs/superpowers/plans/2026-08-03-post-0.1.0-usability.md
index 17cf434..ad6dbc0 100644
--- a/docs/superpowers/plans/2026-08-03-post-0.1.0-usability.md
+++ b/docs/superpowers/plans/2026-08-03-post-0.1.0-usability.md
@@ -77,7 +77,7 @@ taking that too literally.
 | 17 | No completion for tags in the query bar | workflow | M | **done** |
 | 18 | No visual cue that there are unsynced edits | feedback | S | **done** |
 | 19 | No prompt to sync on exit when edits are pending | behavior | S | **done** |
-| 20 | Thread view does not match the user's mental model | presentation | L | built on branch `item-20-message-rows`, **not merged**; see 53 |
+| 20 | Thread view does not match the user's mental model | presentation | L | rebuilt as cards on branch `card-list`, **not merged**; awaiting the user's verdict |
 | 21 | Default shortcuts are not sensible enough | discoverability | S | open |
 | 22 | Translatability audit and i18n wiring | correctness | M | open |
 | 23 | No way to save a search query from the UI | workflow | M | open |
@@ -108,16 +108,16 @@ taking that too literally.
 | 48 | Removing a tag suggests every tag, not the thread's own | workflow | XS | **done** |
 | 49 | Sync runs every account regardless of what changed | workflow | M | **done** |
 | 50 | Esc blanks the pane but leaves the row selected | workflow | XS | **done** |
-| 51 | Clicking a subject scrolls the list sideways | presentation | XS | open; resolved as a side effect of 53, do not work separately |
+| 51 | Clicking a subject scrolls the list sideways | presentation | XS | built on branch `card-list`, **not merged**; a card is viewport width |
 | 52 | `test_querycompleter` fails under Wayland, passes offscreen | testing | XS | **done** |
-| 53 | Message rows still read as a table, not as a conversation | presentation | M | open, specified 2026-08-09; see the card-list spec |
+| 53 | Message rows still read as a table, not as a conversation | presentation | M | built 2026-08-10 on branch `card-list`, **not merged**; awaiting the user's verdict |
 | 54 | A cron sync carries the edits but the count still says pending | correctness | S | **done** |
 | 55 | In a narrow window the message pane is invisible | presentation | XS | **done** |
 | 56 | No action carries an icon, so the toolbar reserves space for nothing | presentation | S | **done** |
 | 57 | "Flag" would read better as "Important" or "Starred" | presentation | XS | **done** |
 | 58 | `message_zoom` documents a 0.5 to 3.0 range and enforces none of it | correctness | XS | **done** |
 | 59 | Archive and Mark all read shipped with the same icon | presentation | XS | **done** |
-| 60 | Next thread dead-ends on the last reply of an expanded thread | defect | XS | open; branch only, fix as part of 53 |
+| 60 | Next thread dead-ends on the last reply of an expanded thread | defect | XS | **done** on the branch; already fixed by 5487d58, see below |
 
 Sizes are rough: XS under an hour, S a sitting, M a session.
 
@@ -3683,11 +3683,23 @@ navigation actions against the same rule.
 current index, which follow visible rows across parent boundaries. For
 thread-to-thread jumping, skip any index whose `IsMessageRole` is true.
 
-**Specified as part of the card-list spec**
-(`docs/superpowers/specs/2026-08-09-card-list-design.md`), which also adds
-Alt+Up/Down for these actions and relies on `QTreeView`'s built-in Up/Down for
-stepping through replies. Fix it there rather than separately, unless the card
-list is dropped.
+**The cause above is wrong, and was corrected on 2026-08-10.** It was read off
+`master`, where the arithmetic really is `current.row() + 1`. The branch does
+not do that: `5487d58` added `MainWindow::threadRowOf()`, which walks up to the
+containing thread BEFORE the arithmetic, so from the last reply of an expanded
+thread `next_thread` already reached the next thread. The defect was fixed in
+the same commit that could have introduced it, one commit before this entry was
+written. Verified by writing both failing tests first, on the branch, and
+watching them pass against unchanged code.
+
+The entry is kept rather than deleted, because the reasoning it records is
+sound and the tests it demanded now exist. It is a reminder that a cause
+"verified in code" is only verified against the branch it was read on.
+
+**Superseded by the card-list work all the same.** Both actions now walk with
+`indexBelow`/`indexAbove` (`card-list`, 2026-08-10), so nothing in that path is
+keyed on a row number, which is the rule a deeper tree would break next.
+Alt+Up/Down were added alongside Ctrl+J/K there.
 
 **Constraint.** The test that would catch this must start from the **last reply
 of an expanded thread**. A test that arrows down a collapsed list passes against
diff --git a/docs/superpowers/plans/2026-08-08-item-20-message-rows.md b/docs/superpowers/plans/2026-08-08-item-20-message-rows.md
index 5935777..f4882c7 100644
--- a/docs/superpowers/plans/2026-08-08-item-20-message-rows.md
+++ b/docs/superpowers/plans/2026-08-08-item-20-message-rows.md
@@ -1,14 +1,5 @@
 # Item 20: Message Rows in the Thread List — Implementation Plan
 
-> **EXECUTED AND PARKED, 2026-08-08. Do not run this plan again.**
-> Every task here was implemented on the branch `item-20-message-rows`, which is
-> pushed to both remotes and **not merged**. master has these documents and none
-> of that code. The user's verdict on the finished result was that the table
-> layout does not fit the use, and item 53 in
-> `2026-08-03-post-0.1.0-usability.md` carries the diagnosis. This document is
-> kept for the API facts it verified and the reasoning it records, not as work
-> to pick up. Read item 53 first.
-
 > **For agentic workers:** REQUIRED SUB-SKILL: Use superpowers:subagent-driven-development (recommended) or superpowers:executing-plans to implement this plan task-by-task. Steps use checkbox (`- [ ]`) syntax for tracking.
 
 **Goal:** Turn the flat thread list into a tree where a thread's root row is its first message, expanding reveals the replies indented by reply depth, and selecting a reply opens that single message in the reading pane.