ci(migrations): confine snapshot cache lookup to a 3-day date window (#285)

* ci(migrations): confine snapshot cache lookup to a 3-day date window

An unbounded prefix restore searches the PR's own ref scope before the
base branch, so one stale PR-scoped snapshot shadows fresh dev-scoped
ones forever (daily CI use keeps it from evicting). PR #280 was pinned
to a 2026-07-10 previewnet snapshot that predates the on-chain
DeregisterAnnouncementPeriod fix and permanently failed the try_state
timing invariant added in #276.

Both jobs now look up snapshots only under explicit dated keys
(today/yesterday/day-before, UTC), so a restored snapshot is at most
two days old regardless of cache scope; the nightly 5AM refresh keeps
PRs from regenerating in practice. Stale branch-scoped entries become
unreachable and evict naturally.

* chore: minimize the docs

Author: danielbui12

.github/workflows/check-runtime-migration.yml

@@ -109,22 +109,29 @@ jobs:
       - name: Load common environment variables via env file
         run: cat .github/env >> $GITHUB_ENV
 
-      # Snapshot lookup uses a deliberately-non-matching primary `key:` so
-      # `restore-keys` always falls through to the most recent dated entry.
-      # With `lookup-only` the snapshot isn't restored — we just decide whether
-      # to regenerate. `cache-matched-key` is empty iff nothing was found, which
-      # is also the case on the daily `schedule` (lookup skipped) so the
-      # snapshot is force-refreshed nightly.
+      # The lookup is date-bounded because an unbounded prefix restore would
+      # let a stale PR-scoped snapshot shadow fresh dev-scoped ones forever.
+      # `cache-matched-key` is empty on a miss and on the nightly `schedule`
+      # (lookup skipped), forcing a snapshot refresh.
+      - name: Compute snapshot date window
+        id: dates
+        shell: bash
+        run: |
+          echo "today=$(/bin/date -u '+%Y%m%d')" >> "$GITHUB_OUTPUT"
+          echo "yesterday=$(/bin/date -u -d '1 day ago' '+%Y%m%d')" >> "$GITHUB_OUTPUT"
+          echo "daybefore=$(/bin/date -u -d '2 days ago' '+%Y%m%d')" >> "$GITHUB_OUTPUT"
+
       - name: Check if snapshot exists in cache
         id: cache-restore
         if: github.event_name != 'schedule'
         uses: actions/cache/restore@55cc8345863c7cc4c66a329aec7e433d2d1c52a9 # v5
         with:
           lookup-only: true
           path: snapshot.raw
-          key: try-runtime-snapshot-${{ matrix.runtime.name }}
+          key: try-runtime-snapshot-${{ matrix.runtime.name }}-${{ steps.dates.outputs.today }}
           restore-keys: |
-            try-runtime-snapshot-${{ matrix.runtime.name }}-
+            try-runtime-snapshot-${{ matrix.runtime.name }}-${{ steps.dates.outputs.yesterday }}
+            try-runtime-snapshot-${{ matrix.runtime.name }}-${{ steps.dates.outputs.daybefore }}
           fail-on-cache-miss: false
 
       - name: Install just
@@ -175,18 +182,12 @@ jobs:
             sleep 10
           done
 
-      - name: Get Date
-        id: get-date
-        if: steps.cache-restore.outputs.cache-matched-key == ''
-        run: echo "today=$(/bin/date -u "+%Y%m%d")" >> "$GITHUB_OUTPUT"
-        shell: bash
-
       - name: Save snapshot to cache
         if: steps.cache-restore.outputs.cache-matched-key == ''
         uses: actions/cache/save@55cc8345863c7cc4c66a329aec7e433d2d1c52a9 # v5
         with:
           path: snapshot.raw
-          key: try-runtime-snapshot-${{ matrix.runtime.name }}-${{ steps.get-date.outputs.today }}
+          key: try-runtime-snapshot-${{ matrix.runtime.name }}-${{ steps.dates.outputs.today }}
 
   check-migrations:
     name: check-migration (${{ matrix.runtime.name }})
@@ -231,11 +232,24 @@ jobs:
         if: steps.try-runtime-cache.outputs.cache-hit != 'true'
         run: just download-try-runtime
 
+      # Same 3-day window as prepare-snapshots: never restore a snapshot more
+      # than two days old, whatever ref scope it lives in.
+      - name: Compute snapshot date window
+        id: dates
+        shell: bash
+        run: |
+          echo "today=$(/bin/date -u '+%Y%m%d')" >> "$GITHUB_OUTPUT"
+          echo "yesterday=$(/bin/date -u -d '1 day ago' '+%Y%m%d')" >> "$GITHUB_OUTPUT"
+          echo "daybefore=$(/bin/date -u -d '2 days ago' '+%Y%m%d')" >> "$GITHUB_OUTPUT"
+
       - name: Restore snapshot from cache
         uses: actions/cache/restore@55cc8345863c7cc4c66a329aec7e433d2d1c52a9 # v5
         with:
           path: snapshot.raw
-          key: try-runtime-snapshot-${{ matrix.runtime.name }}-
+          key: try-runtime-snapshot-${{ matrix.runtime.name }}-${{ steps.dates.outputs.today }}
+          restore-keys: |
+            try-runtime-snapshot-${{ matrix.runtime.name }}-${{ steps.dates.outputs.yesterday }}
+            try-runtime-snapshot-${{ matrix.runtime.name }}-${{ steps.dates.outputs.daybefore }}
           fail-on-cache-miss: true
 
       - name: Run ${{ matrix.runtime.name }} Runtime Checks