fix(drafts): list drafts as messages, not threadssignatures

The Drafts filter shipped threaded in item 138, reasoning that a draft
reply belongs with the conversation it answers. That reasoning cost the
feature: a thread row stands for its first matched message, which for a
draft reply is the message being replied to, so the draft itself had no
row of its own and double-clicking the conversation opened nothing.

Reversed with the user. Drafts now follows Sent; Trash deliberately does
not, since a deleted message still belongs to its conversation and
nothing there has to be reachable for editing.

The view mode was decided in three places that each compared against
"sent" and had to agree: builtinFilter(), the reader that reapplies the
mode, and the writer that skips storing what the generator implies.
generatorIsFlat() is now the one closed set they share, and
builtinFilter() sets flat from it rather than inside a branch so the set
cannot drift from the labels.

Setting only the branch would have looked correct. Its save/load pair
survives by accident, because the writer's skip knew only "sent" and so
would have stored the key for drafts. The gap is the reader's fallback,
for a file carrying no flat key at all: an older build, a migration or a
hand edit comes back threaded against a flat button, and the next save
persists the disagreement.

theDraftsFilterIsThreadedNotFlat is inverted rather than deleted, keeping
its history, and now also pins Trash as threaded. The round trip is
covered by extending aGeneratedEntryWritesNoRedundantKeys, which already
asserted that property for Sent. Mutation-checked: reverting
generatorIsFlat() to "sent" alone fails both.

Suite 37 of 38; undoMovesTheMessageBack is item 136, pre-existing and on
an unrelated path.

Closes item 159.

Co-Authored-By: Claude Opus 5 <noreply@anthropic.com>
Claude-Session: https://claude.ai/code/session_01UUQS6n3cmsFrsjCNmwNtf8

2 files changed, 67 insertions, 0 deletions

diff --git a/docs/superpowers/plans/2026-08-03-post-0.1.0-usability-closed.md b/docs/superpowers/plans/2026-08-03-post-0.1.0-usability-closed.md
index d6adc98..7a52984 100644
--- a/docs/superpowers/plans/2026-08-03-post-0.1.0-usability-closed.md
+++ b/docs/superpowers/plans/2026-08-03-post-0.1.0-usability-closed.md
@@ -7548,3 +7548,68 @@ needed. The drafts view is path-based, so zero tags is exactly enough.
 **Size: S.** One worker slot, one signal, and their tests.
 
 **Closed 2026-08-24** (unreleased). See the status table row for the outcome.
+
+
+## 159. The Drafts view lists threads, so a draft is unreachable by double-click
+
+**Observed (user, 2026-08-25):** "drafts should be treated like \"Sent\",
+listing only actual draft messages and not threads, otherwise I can double
+click on a thread message and nothing happens."
+
+**Cause (verified in code):** `Config::builtinFilter()` in `src/config.cpp`
+sets `filter.flat = true` for the `sent` generator only, at line 1011. The
+`drafts` branch below it leaves the default `false` with a comment stating the
+choice explicitly: "NOT flat, like Trash and unlike Sent: a draft reply
+belongs with the conversation it answers." That was item 138's decision and it
+is the thing the note contradicts.
+
+The consequence the user reports follows from it. A thread row stands for
+`ThreadSummary::firstMessageId`, which in a Drafts view is the first MATCHED
+message of the conversation, and that is not necessarily the draft. Item 153
+gated `edit_draft` on the file living in a configured drafts folder precisely
+so that opening ordinary mail this way cannot make the first autosave delete a
+received message, so the row is inert rather than harmful. Inert is still
+"nothing happens".
+
+**Built 2026-08-25**, after confirming the reversal with the user.
+
+**Not one line, and the reason is the part worth keeping.** The obvious fix is
+`filter.flat = true` in the `drafts` branch. That ships a defect: the view mode
+was decided in THREE places that each hardcoded a comparison against `"sent"`,
+and they have to agree.
+
+- `builtinFilter()` sets it for the button.
+- `loadSavedQueries()` reapplies it on read, so a hand-edited or migrated file
+  cannot produce a threaded Sent view.
+- `saveSavedQueries()` SKIPS writing it when the generator already implies it,
+  because a key carrying no information is one a hand-editor must read past.
+
+Setting only the first does not break the save/load pair, and it is worth being
+exact about why: the writer's skip knew only about `sent`, so it would have
+STORED `"flat": true` for drafts, and the reader would have honoured it. That
+round trip survives by accident.
+
+What does NOT survive is a file that carries no `flat` key: one written by an
+older build, migrated from elsewhere, or hand-edited, which is the case the
+reader's fallback exists for. It comes back THREADED against a flat button, and
+the writer then persists that disagreement on the next save. The reader is the
+load-bearing site, and it is the one a per-branch fix leaves untouched.
+
+`generatorIsFlat()` is the fix: one closed set beside `generatorTag()`, called
+from all three sites. `builtinFilter()` sets `filter.flat` once from it rather
+than inside a branch, so the set cannot drift from the labels below it.
+
+**Trash deliberately did not follow.** A deleted message still belongs to its
+conversation, and nothing in the trash has to be reachable for editing. The
+test asserts this, so a future change that flattens every folder filter fails
+rather than passing quietly.
+
+**Testing.** `theDraftsFilterIsThreadedNotFlat` asserted the old behaviour and
+is inverted rather than deleted, keeping the history in its comment. The
+round-trip is covered by extending `aGeneratedEntryWritesNoRedundantKeys`,
+which already asserted exactly that property for `sent`, rather than by a
+second test that would have restated it. Mutation-checked: reverting
+`generatorIsFlat()` to `sent` alone fails both.
+
+Suite 37 of 38; the failure is `undoMovesTheMessageBack`, item 136,
+pre-existing and on an unrelated path.
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 2d99704..4aeff26 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
@@ -230,6 +230,8 @@ taking that too literally.
 
 | 158 | A freshly saved draft is invisible until a sync indexes it | defect | S | **done** 2026-08-24, unreleased. `saveDraftNow()` emits `draftSaved`, which `MainWindow` connects to a new `NotmuchWorker::indexDraftFile()` that indexes the one file (previous revision removed, so a rewrite leaves no ghost), and `draftRemoved` drops the entry when a sent draft is unlinked. Measured: `index_file` assigns NO tags, so no stripping and no tag:inbox leak. See the section |
 
+| 159 | The Drafts view lists threads, so a draft is unreachable by double-click | defect | S | **done** 2026-08-25, unreleased. Reverses item 138's own decision, confirmed with the user. `generatorIsFlat()` in `config.cpp` is now the single closed set of flat generators, replacing three hardcoded comparisons against `"sent"`: the built-in filter, the reader that reapplies the mode, and the writer that skips storing what the generator implies. Those three had to agree and nothing made them; a `drafts` entry saved and reloaded would otherwise have come back THREADED while the button was flat. `builtinFilter()` sets `flat` once from the helper rather than in a branch, so the set cannot drift from the labels |
+
 Sizes are rough: XS under an hour, S a sitting, M a session.
 
 ---