tasks: make the tasks-page test fixtures $TZ-stable (#1808)

docs/changes/unreleased/1809-tz-stable-tasks-heading-test.md

@@ -0,0 +1,26 @@
+---
+kind: internal
+title: the tasks-page test fixtures pin their clocks to the local zone, so they no longer fail east of UTC
+pr: 1809
+surface: [chat]
+invalidates:
+  - >-
+    The tasks-page tests were believed to be deterministic and host-independent.
+    They built their fixture clocks in a fixed -04:00 zone while the tasks window
+    buckets days in the viewer's LOCAL zone (usageBucketStart, and the "THE DAY
+    IS THE WRITER'S" law on SpendToday), so a date the tests assert — the chat
+    manual's `since aug 11`, and the `shift+← aug 2 – aug 25 →` window control —
+    shifted by a day once the foreign offset was read as local on a host far
+    enough east: green on a UTC runner, red on a UTC+8 box (#1808). Every
+    tasks-page fixture clock is now built in time.Local, so the tests read the
+    same dates under every $TZ.
+---
+
+No product behavior changed: the window following the viewer's local calendar
+day is deliberate and stays. The tests were host-dependent because each fixture
+injected a fixed -04:00 clock and then asserted dates that only matched in the
+author's timezone band — one shared cause across tallyrows_test.go,
+tasksplace_test.go, tasksparked_test.go, tasksconversation_test.go and
+taskstable_test.go, two of whose tests were already red on a UTC+8 box.
+Verified identical green from Pacific/Pago_Pago (UTC-11) to Pacific/Kiritimati
+(UTC+14).

internal/tui3/tallyrows_test.go

@@ -210,7 +210,15 @@ func TestTheTasksFootStillCountsEveryPieceByItsActualState(t *testing.T) {
 // branches and the corpus is asked for what they produced, so neither heading can
 // be restated as a literal that drifts.
 func TestTheManualQuotesBothTasksOpeningHeadingsExactly(t *testing.T) {
-	loc := time.FixedZone("fixture", -4*60*60)
+	// The window buckets days in the viewer's LOCAL zone, on purpose: spend and
+	// subtask counts are attributed to the writer's own calendar day (session's
+	// usageBucketStart, and the "THE DAY IS THE WRITER'S" law on SpendToday). So
+	// the fixture clock has to live in that same zone, or the rendered `since`
+	// date — which the chat manual quotes verbatim — shifts by a day on any host
+	// where a fixed foreign offset crosses midnight once read as local. A
+	// `-04:00` clock did exactly that: green on a UTC runner, red on a UTC+8 box,
+	// `aug 11` versus `aug 12` (#1808).
+	loc := time.Local
 	now := time.Date(2026, time.August, 25, 13, 11, 0, 0, loc)
 	win := session.LastDays(now, 15)
 

internal/tui3/tasksconversation_test.go

@@ -33,7 +33,7 @@ import (
 // is the depth the old page could not draw. `thor clips` finished yesterday and
 // has nothing under it but one row.
 func tasksChatFixture() (session.World, session.UsageWindow, time.Time) {
-	loc := time.FixedZone("fixture", -4*60*60)
+	loc := time.Local // #1808: the window buckets in local time, so a fixed foreign offset would shift the dates by $TZ
 	now := time.Date(2026, time.September, 6, 13, 0, 0, 0, loc)
 	ago := func(d time.Duration) time.Time { return now.Add(-d) }
 

internal/tui3/tasksparked_test.go

@@ -21,7 +21,7 @@ import (
 // one piece of work waiting on a person, and two admitted behind it that nothing
 // has started.
 func tasksParkedFixture() (session.World, session.UsageWindow, time.Time) {
-	loc := time.FixedZone("fixture", -4*60*60)
+	loc := time.Local // #1808: the window buckets in local time, so a fixed foreign offset would shift the dates by $TZ
 	now := time.Date(2026, time.September, 2, 23, 52, 0, 0, loc)
 	row := session.SessionRow{ID: "room-a", Title: "The Task Surface", Project: "codeaf", Open: true, Live: false}
 	entry := func(id, label, status string) session.TaskIndexEntry {

internal/tui3/tasksplace_test.go

@@ -17,7 +17,7 @@ import (
 var tasksWidths = []int{60, 80, 120, 200}
 
 func tasksFixture() (session.World, session.UsageWindow, time.Time) {
-	loc := time.FixedZone("fixture", -4*60*60)
+	loc := time.Local // #1808: the window buckets in local time, so a fixed foreign offset would shift the dates by $TZ
 	now := time.Date(2026, time.August, 25, 13, 11, 0, 0, loc)
 	at := func(day, hour int) time.Time { return time.Date(2026, time.August, day, hour, 0, 0, 0, loc) }
 	entry := func(id, label, status string, ended time.Time, cost float64) session.TaskIndexEntry {
@@ -381,7 +381,7 @@ func TestTasksChangedSinceCountsOnlyLandedWorkAfterTheLook(t *testing.T) {
 // that landed today with three workers under it, and a second root beside it
 // that is nobody's family.
 func tasksFamilyFixture() (session.World, session.UsageWindow, time.Time) {
-	loc := time.FixedZone("fixture", -4*60*60)
+	loc := time.Local // #1808: the window buckets in local time, so a fixed foreign offset would shift the dates by $TZ
 	now := time.Date(2026, time.August, 25, 13, 11, 0, 0, loc)
 	at := func(hour int) time.Time { return time.Date(2026, time.August, 25, hour, 0, 0, 0, loc) }
 	row := session.SessionRow{ID: "room-a", Title: "The Split", Project: "codeaf", Open: true}
@@ -573,7 +573,7 @@ func TestVisibleChildrenKeepTheirOwnSectionsWhenTheRootIsAbsent(t *testing.T) {
 // detail beside each — and arriving OUT of time order, which is what the world
 // scan hands this place.
 func tasksPolishFixture() (session.World, session.UsageWindow, time.Time) {
-	loc := time.FixedZone("fixture", -4*60*60)
+	loc := time.Local // #1808: the window buckets in local time, so a fixed foreign offset would shift the dates by $TZ
 	now := time.Date(2026, time.September, 2, 23, 3, 0, 0, loc)
 	done := func(id, label, outcome string, files int, cost float64, ago time.Duration) session.TaskIndexEntry {
 		return session.TaskIndexEntry{
@@ -956,7 +956,7 @@ func TestTheTaskPageNamesTheConversationItCameOutOf(t *testing.T) {
 // [homeName], whose title case has raised the id's first letter), so the
 // composer keys on the trimmed title equal to the row's own id, folded.
 func TestAConversationWithNoTitleIsCalledTheWordNotItsId(t *testing.T) {
-	loc := time.FixedZone("fixture", -4*60*60)
+	loc := time.Local // #1808: the window buckets in local time, so a fixed foreign offset would shift the dates by $TZ
 	now := time.Date(2026, time.September, 11, 14, 25, 0, 0, loc)
 	id := "de9ea39e6f4c18c3"
 	transcript := "/private/tmp/htw/codeaf/" + id + "/transcript.jsonl"

internal/tui3/taskstable_test.go

@@ -18,7 +18,7 @@ import (
 // their headings, and the rows inside one of them have three different prices so
 // that descending is distinguishable from arriving.
 func tasksTableFixture() (session.World, session.UsageWindow, time.Time) {
-	loc := time.FixedZone("fixture", -4*60*60)
+	loc := time.Local // #1808: the window buckets in local time, so a fixed foreign offset would shift the dates by $TZ
 	now := time.Date(2026, time.September, 11, 12, 0, 0, 0, loc)
 	ago := func(d time.Duration) time.Time { return now.Add(-d) }
 	work := func(room, id, label, status string, ended time.Time, files int, cost float64) session.TaskIndexEntry {