Reuse weekly schedule post instead of reposting

The Monday rollover deleted last week's schedule message and posted a
fresh one every week, which re-notified the channel, changed the
permalink, and dropped any thread/reactions. Roll the two-week window
forward by editing the stored message in place (the same chat_update
path in-week shift changes already use), falling back to a fresh, pinned
post on first run or when the edit fails. A native pin keeps it reachable
from the channel header now that it no longer rises on the weekly repost.

Records the evaluation behind this in docs/sticky-schedule-post.md.

Refs: #135

CHANGELOG.md

@@ -10,6 +10,18 @@ fine and still supported.
 
 ---
 
+## v1.13.0 — June 27, 2026
+
+**The two-week schedule post now stays put instead of being reposted every
+week.** Each Monday the bot used to delete last week's schedule message and post
+a brand-new one — which pinged the channel again, changed the message's link,
+and dropped any replies or reactions. Now it simply edits the existing post to
+roll the two-week window forward, so the link stays stable, there's no weekly
+re-notification, and any thread stays attached. The post is also pinned, so you
+can always reach it from the channel header even after a busy day of chat. (The
+pin needs a one-time app reinstall to switch on; until then everything else still
+works.)
+
 ## v1.12.0 — June 26, 2026
 
 **Clearer shift drops and an easier-to-read schedule.** Two small quality-of-life

docs/sticky-schedule-post.md

@@ -0,0 +1,114 @@
+# Evaluation: sticky / reused weekly schedule post
+
+_Spike for issue #135 — decide how the Monday two-week schedule post should
+behave across weeks. This document records the decision and the rationale; the
+recommended option (a) is implemented in the same PR._
+
+## Background
+
+`src/weekly-post/app.py` (the Monday 7am ET Lambda) currently, every week:
+
+1. `chat_delete` the previous week's schedule post (stored `ts` from
+   `get_schedule_post`),
+2. `chat_postMessage` a brand-new two-week schedule message, and
+3. `save_schedule_post(channel_id, new_ts, …)`.
+
+So every Monday the post gets a new `ts` (new permalink), re-notifies the
+channel, and loses any thread/reactions. During the week it steadily sinks as
+people chat.
+
+The infrastructure to edit in place **already exists**: in-week shift changes
+(`pick` / `drop` / `swap` / `admin`) call `_refresh_schedule_post()`
+(`src/slack-bot/app.py`), which does a `chat_update` against the stored `ts`.
+The weekly rollover is the *only* place that creates a fresh message.
+
+## Options considered
+
+### (a) Reuse the same post across weeks — **recommended**
+
+On Monday, `chat_update` the existing message to roll the two-week window
+forward instead of delete + repost.
+
+- **Pros:** stable permalink; no weekly re-notification; keeps any
+  thread/reactions; trivial change (reuses the `_refresh_schedule_post`
+  `chat_update` pattern already in the codebase).
+- **Cons:** the message stays where it was first posted — it does **not** rise
+  to the bottom as the channel gets new activity.
+
+### (b) True stickybot behavior — keep it pinned to the bottom
+
+Slack has no native "sticky" message. Stickybot-style bots subscribe to channel
+message events and **delete + repost** the bot message whenever someone else
+posts, so it is always last.
+
+- **Pros:** always visible at the bottom of the channel.
+- **Cons:** directly conflicts with (a)'s stable permalink (every repost = new
+  `ts`); requires a new event subscription (`message.channels`) and the
+  `channels:history` scope (a reinstall); needs dedupe/debounce plus Slack
+  rate-limit handling; constant repost churn; many more moving parts and a new
+  always-on event path to operate. The benefit (bottom-of-channel visibility)
+  is marginal for a low-traffic on-call channel.
+
+### (c) Status quo — delete + repost weekly
+
+- **Pros:** the weekly repost bumps the post to the bottom once a week.
+- **Cons:** new permalink every week; a weekly re-notification; loses
+  thread/reactions; the post still sinks for the rest of the week.
+
+## Decision
+
+Adopt **(a) reuse-in-place**, complemented by a **native Slack pin** so the post
+stays reachable from the channel header even as the channel fills with chatter.
+Reject **(b)** — its only advantage over a pin is keeping the post at the literal
+bottom, which is not worth a new event subscription, an extra scope, and
+rate-limit/debounce machinery for this channel. The pin recovers most of the
+discoverability that the weekly bump used to provide, at the cost of one extra
+API call and one extra scope (`pins:write`), with no new event path to operate.
+
+## What changes (option a)
+
+In `src/weekly-post/app.py`, on the Monday rollover:
+
+- **Drop the unconditional `chat_delete`.** There is no previous message to
+  remove when we reuse the same one.
+- **`chat_update` the stored post** to roll the two-week window forward, keeping
+  the same `ts` (stable permalink, no re-notification).
+- **First-run / recovery fallback:** when there is no stored post, or the
+  `chat_update` fails (e.g. the message was deleted manually), fall back to
+  `chat_postMessage` and **pin** the new message.
+- **Keep `save_schedule_post` / `get_schedule_post`.** Still needed — they hold
+  the `ts` that both the weekly rollover and `_refresh_schedule_post` edit. On
+  reuse the stored `ts` is unchanged; on a fresh post it is updated to the new
+  `ts` and the new `week_start`.
+
+### Interaction with `_refresh_schedule_post`
+
+No change needed. Both paths now converge on a single long-lived message keyed
+by the stored `ts`: the weekly Lambda rolls the window forward each Monday, and
+in-week shift changes keep editing the same message. They never fight because
+neither creates a new `ts` while one already exists.
+
+### The "ever-growing edited message" / retention question
+
+A `chat_update` does not grow channel history — it rewrites one message in place
+rather than appending. Slack keeps the message's original post time, so an
+edited-forever post sorts by where it was first posted (hence the pin). There is
+no retention or history-size concern from editing the same message indefinitely.
+
+## Scope / manifest impact
+
+- `pins:write` is added to `slack-app-manifest.yaml` for the native pin. This is
+  a new OAuth scope, so the app must be **reinstalled** once for the pin to take
+  effect. The pin call is best-effort: until the reinstall happens (or if the
+  bot lacks the scope) it logs and is skipped, and the reuse-in-place behavior
+  still works without it.
+- No new event subscriptions. Option (b)'s `message.channels` event and
+  `channels:history` scope are **not** added.
+
+## Follow-ups (not in this PR)
+
+- After deploy, reinstall the Slack app so `pins:write` takes effect, then
+  confirm the first rolled-forward post gets pinned.
+- Optional: a one-line threaded note on the rolled-forward post if we later
+  decide we still want a light weekly nudge (kept out here on purpose — the whole
+  point of (a) is to stop the weekly re-notification).

slack-app-manifest.yaml

@@ -5,11 +5,14 @@
 # reconcile it against the live app config (App settings → App Manifest) so no
 # existing scope or setting is dropped.
 #
-# The ONLY delta this release introduces is the App Home tab:
+# This release adds the bot `pins:write` scope so the Monday rollover can natively
+# pin the reused two-week schedule post. A new OAuth scope means a one-time
+# reinstall is required for the pin to take effect (the pin is best-effort and is
+# skipped until then). Replace <API_URL> with the SlackBotApiUrl stack output.
+#
+# A prior release added the App Home tab (no new scope):
 #   - settings.event_subscriptions.bot_events: + app_home_opened
 #   - features.app_home.home_tab_enabled: true
-# Neither needs a new OAuth scope, so no reinstall is required (see README →
-# "Releases & versioning"). Replace <API_URL> with the SlackBotApiUrl stack output.
 display_information:
   name: After-Hours Shift Manager
   description: Manage after-hours on-call phone duty from Slack.
@@ -36,6 +39,10 @@ oauth_config:
       - chat:write
       - im:write
       - users:read
+      # pins:write lets the Monday rollover natively pin the reused schedule post
+      # so it stays reachable from the channel header. Adding it requires a
+      # one-time reinstall; the pin is best-effort until then.
+      - pins:write
 
 settings:
   event_subscriptions:

src/slack-bot/CHANGELOG.md

@@ -10,6 +10,18 @@ fine and still supported.
 
 ---
 
+## v1.13.0 — June 27, 2026
+
+**The two-week schedule post now stays put instead of being reposted every
+week.** Each Monday the bot used to delete last week's schedule message and post
+a brand-new one — which pinged the channel again, changed the message's link,
+and dropped any replies or reactions. Now it simply edits the existing post to
+roll the two-week window forward, so the link stays stable, there's no weekly
+re-notification, and any thread stays attached. The post is also pinned, so you
+can always reach it from the channel header even after a busy day of chat. (The
+pin needs a one-time app reinstall to switch on; until then everything else still
+works.)
+
 ## v1.12.0 — June 26, 2026
 
 **Clearer shift drops and an easier-to-read schedule.** Two small quality-of-life

src/weekly-post/app.py

@@ -247,6 +247,16 @@ def _send_pay_email(week_label: str, pay_record: dict) -> None:
     logger.info("Sent pay email to %s", recipients)
 
 
+def _pin_schedule_post(slack, channel_id, message_ts):
+    """Best-effort native pin so a freshly posted schedule stays reachable from
+    the channel header even as the channel fills with chatter."""
+    try:
+        slack.pins_add(channel=channel_id, timestamp=message_ts)
+        logger.info("Pinned schedule post %s", message_ts)
+    except Exception:
+        logger.info("Could not pin schedule post %s", message_ts, exc_info=True)
+
+
 def handler(event, context):
     now = datetime.now(EASTERN)
 
@@ -307,35 +317,57 @@ def handler(event, context):
                 week_key,
             )
 
-    # --- Delete previous week's schedule post ---
-    old_post = schedule.get_schedule_post(channel_id)
-    if old_post and old_post.get("message_ts"):
-        try:
-            slack.chat_delete(channel=channel_id, ts=old_post["message_ts"])
-            logger.info("Deleted previous schedule post %s", old_post["message_ts"])
-        except Exception:
-            logger.warning("Could not delete old schedule post", exc_info=True)
-
     # --- Two-week schedule (always starts on Monday of this week) ---
     this_monday = now - timedelta(days=now.weekday())
+    week_start = this_monday.strftime("%Y-%m-%d")
     blocks = build_week_schedule(schedule, start_date=this_monday)
 
     end_date = this_monday + timedelta(days=13)
-    result = slack.chat_postMessage(
-        channel=channel_id,
-        blocks=blocks,
-        text=f"After-Hours Schedule — {this_monday.strftime('%b %-d')} to {end_date.strftime('%b %-d')}",
+    fallback_text = (
+        f"After-Hours Schedule — {this_monday.strftime('%b %-d')} "
+        f"to {end_date.strftime('%b %-d')}"
     )
 
-    schedule.save_schedule_post(
-        channel_id, result["ts"], this_monday.strftime("%Y-%m-%d")
-    )
-    logger.info(
-        "Posted weekly schedule to channel %s (ts=%s)", channel_id, result["ts"]
-    )
+    # Reuse the same post across weeks: roll the two-week window forward by
+    # editing the existing message in place (stable permalink, no weekly
+    # re-notification, keeps any thread/reactions) instead of delete + repost.
+    # Fall back to a fresh, pinned post when there is no stored message or the
+    # edit fails (e.g. the message was deleted manually).
+    old_post = schedule.get_schedule_post(channel_id)
+    message_ts = None
+    if old_post and old_post.get("message_ts"):
+        try:
+            slack.chat_update(
+                channel=channel_id,
+                ts=old_post["message_ts"],
+                blocks=blocks,
+                text=fallback_text,
+            )
+            message_ts = old_post["message_ts"]
+            logger.info(
+                "Rolled schedule post %s forward to week of %s",
+                message_ts,
+                week_start,
+            )
+        except Exception:
+            logger.warning(
+                "Could not update existing schedule post; reposting", exc_info=True
+            )
+
+    if message_ts is None:
+        result = slack.chat_postMessage(
+            channel=channel_id, blocks=blocks, text=fallback_text
+        )
+        message_ts = result["ts"]
+        _pin_schedule_post(slack, channel_id, message_ts)
+        logger.info(
+            "Posted new weekly schedule to channel %s (ts=%s)", channel_id, message_ts
+        )
+
+    schedule.save_schedule_post(channel_id, message_ts, week_start)
     return {
         "posted": True,
         "channel": channel_id,
-        "message_ts": result["ts"],
+        "message_ts": message_ts,
         "pay_calculated": bool(pay_record["breakdown"]),
     }

tests/weekly_post/test_handler.py

@@ -82,11 +82,42 @@ def test_pay_email_failure_does_not_block_schedule_post(
 
 
 @freeze_time(MON_0800)
-def test_deletes_previous_schedule_post(weeklypost_app, schedule, seed, slack, env):
+def test_rolls_existing_post_forward(weeklypost_app, schedule, seed, slack, env):
+    # An existing post is edited in place (stable permalink), never deleted.
     seed.schedule_post("C_TEST", "111.111")
-    weeklypost_app.handler({"force": True}, None)
-    slack.chat_delete.assert_called_once()
-    assert slack.chat_delete.call_args.kwargs["ts"] == "111.111"
+    result = weeklypost_app.handler({"force": True}, None)
+
+    slack.chat_delete.assert_not_called()
+    slack.chat_update.assert_called_once()
+    assert slack.chat_update.call_args.kwargs["ts"] == "111.111"
+    # The stored ts is unchanged, so the permalink stays stable.
+    assert result["message_ts"] == "111.111"
+    assert schedule.get_schedule_post("C_TEST")["message_ts"] == "111.111"
+
+
+@freeze_time(MON_0800)
+def test_pins_post_on_first_run(weeklypost_app, schedule, seed, slack, env):
+    # No existing post → post a fresh message and natively pin it.
+    result = weeklypost_app.handler({"force": True}, None)
+
+    slack.chat_postMessage.assert_called()
+    slack.pins_add.assert_called_once()
+    assert slack.pins_add.call_args.kwargs["timestamp"] == "999.000"
+    assert result["message_ts"] == "999.000"
+
+
+@freeze_time(MON_0800)
+def test_reposts_when_update_fails(weeklypost_app, schedule, seed, slack, env):
+    # A stored post that can no longer be edited (e.g. deleted manually) falls
+    # back to a fresh, pinned post and re-saves the new ts.
+    seed.schedule_post("C_TEST", "111.111")
+    slack.chat_update.side_effect = Exception("message_not_found")
+
+    result = weeklypost_app.handler({"force": True}, None)
+
+    slack.pins_add.assert_called_once()
+    assert result["message_ts"] == "999.000"
+    assert schedule.get_schedule_post("C_TEST")["message_ts"] == "999.000"
 
 
 @freeze_time(MON_0800)