Show the deployed commit as a hover tooltip on the topbar brand

ASSET_VERSION only proves *a* deploy happened recently, not *which*
commit -- not enough to answer "did my push actually deploy, or am I
looking at a stale browser cache" (today's actual answer: neither --
deploy was current, a GeoJSON cache predating a code change was just
never invalidated, since it only checks the source .gpx's mtime).

The CI deploy job now writes REVISION (short SHA) before dropping
.git; app.rb reads it at boot, falling back to "dev" locally/in CI's
own check job where the file never exists.

.gitea/workflows/ci.yml

@@ -54,6 +54,14 @@ jobs:
             fetch --depth 1 origin "${{ gitea.sha }}"
           git checkout -q FETCH_HEAD
 
+      # Read by app.rb at boot and shown (as a hover tooltip on the topbar
+      # brand) so it's possible to tell which commit is actually live
+      # without digging through `tea actions runs list` — written here,
+      # before .git gets dropped below, since that's otherwise the only
+      # place the commit is recorded.
+      - name: Write REVISION
+        run: git rev-parse --short HEAD > REVISION
+
       # Clears out everything in the target except data/ (uploaded GPX
       # files, offline.pmtiles) and copies the fresh checkout over, dropping
       # .git afterwards. Dotfiles like .env (deployment secrets) are left

.gitignore

@@ -29,3 +29,7 @@
 # Deployment secrets (SESSION_SECRET, Gitea OAuth2 client id/secret) — lives
 # only on the server, see docs/deployment.adoc
 .env
+
+# Written by the CI deploy job with the commit it deployed — never
+# committed itself, see app.rb's REVISION
+/REVISION

app.rb

@@ -39,6 +39,20 @@ module Maptool
     # the container) is enough — it doesn't need to survive restarts.
     ASSET_VERSION = Time.now.to_i
 
+    # Written by the CI deploy job (.gitea/workflows/ci.yml) right before it
+    # drops .git from the deployed copy, so this is the only way to tell
+    # which commit is actually live short of asking the deploy job itself —
+    # handy for exactly the kind of "did my push actually deploy, or am I
+    # looking at a stale browser cache" confusion ASSET_VERSION above can't
+    # answer by itself (that only proves *a* deploy happened recently, not
+    # *which* one). Absent outside a real deploy (local dev, CI's own
+    # `check` job), hence the fallback.
+    REVISION = begin
+      File.read(File.join(__dir__, "REVISION")).strip
+    rescue Errno::ENOENT
+      "dev"
+    end
+
     # Overridable so the test suite can point this at a throwaway directory
     # instead of the real data/ — nothing else needs to set this.
     DATA_DIR = ENV.fetch("MAPTOOL_DATA_DIR") { File.join(__dir__, "data") }
@@ -151,7 +165,7 @@ module Maptool
     end
 
     get "/" do
-      erb :index, locals: { logged_in: logged_in?, user: session[:user] }
+      erb :index, locals: { logged_in: logged_in?, user: session[:user], revision: REVISION }
     end
 
     get "/api/health" do

views/index.erb

@@ -1,6 +1,6 @@
 <div id="app">
   <header class="topbar">
-    <span class="topbar__brand">MapTool</span>
+    <span class="topbar__brand" title="rev <%= revision %>">MapTool</span>
     <div class="topbar__auth">
       <% if logged_in %>
         <span><%= user %></span>