feat(compose): open a draft to finish it

Item 153. DraftStore had a write() and no reader, and nothing opened a
composer from an existing message, so a draft rendered like ordinary mail
and could never be finished or sent.

ComposeContextBuilder::forDraft() reads one back. A new Kind::Draft seeds
every field verbatim: the subject takes no Re:/Fwd: prefix, and the body
goes in exactly as it was left, with none of seedBody()'s quote framing. It
is reachable by double-click and by an edit_draft action in the Message
menu.

Three things the shape of this depends on.

A resumed draft must OWN its file. Maildir has no in-place edit, so an
autosave writes a new file and unlinks the old one; a composer that did not
know its own path would leave the original behind and one message would
become two. ComposeContext::draftPath carries it into m_draftPath, which the
autosave already knew how to replace.

MimeParser had no bcc, and nothing had ever needed one. MessageBuilder
writes Bcc into the draft file deliberately and explains why, so a resumed
draft that ignored it would drop every blind recipient from the message the
user then finishes and sends, reporting nothing.

edit_draft is gated on the file being inside a configured drafts folder,
matched on the PATH. A `draft` tag is not enough: notmuch surfaces the
Maildir D flag as one, and a message flagged by another client sits in the
inbox. Offered on ordinary mail, the composer would own a file it did not
write and the first autosave would delete a received message.

And a live defect found on the way, which is most of why this took as long
as it did. updateComposeActions() ran only from onSelectionChanged. Both
signals fire for an ordinary click, so nothing had noticed; but running a
query and setting the current index emits currentRowChanged ALONE, so the
enablement was computed against the previously selected row. Edit draft
stayed disabled on a draft selected that way, and the reply family had the
same blind spot with no test that could see it. Now connected to both.
Reading currentRowChanged is safe here for the reason CLAUDE.md gives: it
answers "which row is current", and no count is read.

WorkerBackedWindow::AccountSpec gains a drafts field, which the two new
tests need and which no fixture could express before.

1 files changed, 44 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 133a761..0f7181b 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
@@ -7348,3 +7348,47 @@ what a drafts folder is; they are separate readers and neither should start
 importing the other.
 
 ---
+
+## 153. A draft cannot be opened for editing, so it is write-only
+
+**Observed (user, 2026-08-24).** Found the moment item 138 gave drafts a
+button: "Double clicking on a draft should open the message in the editor
+window", and "there's no edit action anywhere, a draft is useless as is".
+
+**Cause (verified in code).** `DraftStore` had a `write()` and no reader, and
+nothing anywhere opened a composer from an existing message. A draft therefore
+rendered in the message pane like ordinary mail and could never be finished.
+
+**Outcome.** `ComposeContextBuilder::forDraft()`, a `Kind::Draft` that seeds
+every field verbatim, `edit_draft` in the Message menu, and double-click.
+
+**Three things worth keeping.**
+
+**A resumed draft must own its file.** Maildir has no in-place edit, so an
+autosave writes a new file and unlinks the old; a composer that did not know
+its own path would leave the original behind and one message would become two.
+`ComposeContext::draftPath` carries it into `m_draftPath`, which the autosave
+already knew how to replace.
+
+**`MimeParser` had no `bcc` and nothing had ever needed one.**
+`MessageBuilder` writes Bcc into the draft file deliberately and says why, so a
+resumed draft that ignored it would drop every blind recipient from the message
+the user then finishes and sends, silently. That is the failure this item was
+most likely to ship.
+
+**The gate is not cosmetic.** `edit_draft` is offered only on a file inside a
+configured drafts folder, matched on the PATH: a `draft` tag is not enough,
+since notmuch surfaces the Maildir D flag as one and a message flagged by
+another client sits in the inbox. Offered on ordinary mail, the composer would
+own a file it did not write and the first autosave would DELETE a received
+message.
+
+**And a live defect found on the way, which is the reason this took as long as
+it did.** `updateComposeActions()` ran only from `onSelectionChanged`. Both
+signals fire for an ordinary click, so nothing had ever noticed; but running a
+query and setting the current index emits `currentRowChanged` ALONE, so the
+enablement was computed against the previously selected row. Measured: Edit
+draft stayed disabled on a draft selected that way, and the reply family had
+the same blind spot without a test that could see it. It is now connected to
+both signals. Reading `currentRowChanged` is safe here for the reason
+`CLAUDE.md` gives: it answers "which row is current", and no count is read.