1 files changed, 27 insertions, 1 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 656773b..26464ba 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
@@ -117,7 +117,7 @@ taking that too literally.
 | 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 | **done**; already fixed by 5487d58, see below |
-| 61 | `test_mainwindow` fails intermittently, about 1 run in 20 | testing | S | open; cause established 2026-08-11 (the user's cron sync holds the mbsync lock), fix is item 38's seam applied suite-wide |
+| 61 | `test_mainwindow` fails intermittently, about 1 run in 20 | testing | S | **done** 2026-08-13; an `init()` fixture points every test at its own lock table |
 | 62 | No config option for the date format on a card | presentation | XS | **done** 2026-08-11 |
 | 63 | No way to see sent mail, and no filter for it | workflow | M | **done** 2026-08-11; see `specs/2026-08-11-sent-mail-design.md` |
 | 64 | The Sync button carries a mailbox icon, not a refresh one | presentation | XS | **done** 2026-08-11 |
@@ -4125,6 +4125,32 @@ initially mistaken for a regression that change had introduced.
 
 **Size: S**, most of it in reproducing reliably rather than in the fix.
 
+### Outcome (done 2026-08-13)
+
+`TestMainWindow::init()` builds a `QTemporaryDir` per test and points
+`MainWindow::setLocksPathForTesting` at an empty file inside it, so no test
+reads the real `/proc/locks`. An empty table is the honest representation of
+"no sync is running"; the three tests that want to observe a sync write their
+own content, as they already did.
+
+**The three existing users of the seam each restored `"/proc/locks"` when they
+finished, and that restoration was itself a defect**: it handed the real table
+back to whichever test ran next, so one test opting in re-exposed every test
+after it. All three restores are removed, and `cleanup()` deliberately leaves
+the path pointing at the temporary file.
+
+`noTestCanSeeTheRealLockTable` guards the fixture, since a suite that silently
+reverts to the real table would go back to failing for reasons no assertion
+mentions.
+
+Verified rather than assumed, using the reproduction above. With
+`flock /tmp/mbsync.lock -c 'sleep 30'` held: 3 failures before
+(`aRefreshDoesNotStampOverASelectionMessage`,
+`anActionOnAMessageRowTagsThatMessageNotTheThread`,
+`aSuccessfulCronSyncDrainsTheEditedAccounts`), 119/119 after, and the full suite
+19/19 with the lock held. Mutation-checked by disabling the fixture: the guard
+fails first with its diagnostic, and a real test fails behind it.
+
 ## 62. No config option for the date format on a card
 
 **Observed (user, from the notes):** "option in config file for date format".