Sign debug builds with a shared, checked-in keystore

"App not installed" when updating. Android generates a debug keystore per
machine, so tungsten's build and the laptop's build are signed differently and
each refuses to install over the other. Reproduced exactly:
INSTALL_FAILED_UPDATE_INCOMPATIBLE, "signatures do not match newer version".

The published APKs show the collision plainly -- 0930d0 on the 21st, 106ecafe
in between, 0930d0 again after my last publish -- so an update had roughly a
coin-flip chance of being installable depending on which machine built it.

The checked-in key is tungsten's existing debug keystore, stock alias and
password, not a freshly generated one. That matters: a new key would have been
just as unusable as the mismatch, forcing a second uninstall and a second loss
of every playback position, right after Peter had already done one. Verified by
installing the currently-published APK and updating in place over it.

Safe to commit -- it signs debug builds of a personal sideloaded app. It must
never sign a release, where the key is the app's identity.

Co-Authored-By: Claude Opus 5 <noreply@anthropic.com>
Claude-Session: https://claude.ai/code/session_018AwnALZL6bD4VBtATDVv3B

3 files changed, 34 insertions, 0 deletions

diff --git a/CLAUDE.md b/CLAUDE.md
index f97e524..8308bb8 100644
--- a/CLAUDE.md
+++ b/CLAUDE.md
@@ -155,6 +155,14 @@ skipping. `skipIntroMs`/`skipOutroMs` exist on `SubscriptionEntity` and nothing
   Twice the better answer was restructuring instead: `Screens.kt` was split per screen and
   `ListenViewModel` was split into library and player halves rather than raising a limit again.
 
+- **Debug builds are signed with the checked-in `keystore/listen-debug.keystore`**, not the
+  per-machine one Android generates. Two machines build this app, and differently-signed APKs
+  refuse to install over each other: "App not installed", or
+  `INSTALL_FAILED_UPDATE_INCOMPATIBLE`, with the only remedy an uninstall that destroys every
+  playback position. The checked-in file is tungsten's original debug keystore, with the stock
+  alias and password, because that is the key already on the phone. Never swap it for a fresh
+  one — that costs another uninstall. Never use it for a release.
+
 - **Feeds are big.** A real subscription in testing produced 2753 episodes in one refresh. Any
   per-episode work — a query in a loop, an O(n²) match — needs to be considered at that scale.
 
diff --git a/app/build.gradle.kts b/app/build.gradle.kts
index f680a08..a81df9b 100644
--- a/app/build.gradle.kts
+++ b/app/build.gradle.kts
@@ -37,6 +37,32 @@ android {
 
     }
 
+    signingConfigs {
+        // A checked-in debug key, deliberately.
+        //
+        // Android generates a per-machine debug keystore, so a build from tungsten and a build
+        // from the laptop are signed differently and each refuses to install over the other --
+        // "App not installed", with the only remedy being an uninstall that destroys every
+        // playback position. Two machines build this app, so the key has to be shared.
+        //
+        // This is tungsten's existing debug keystore rather than a fresh one, chosen because
+        // that is the key already installed on the phone -- a new key would have forced a
+        // second uninstall and a second loss of every playback position.
+        //
+        // Safe to commit: it signs debug builds of a personal sideloaded app and nothing else.
+        // It must never be used for a Play release, where the signing key is the app's identity.
+        getByName("debug") {
+            storeFile = file("$rootDir/keystore/listen-debug.keystore")
+            // Android's standard debug credentials: this IS the platform debug keystore,
+            // copied in so both machines sign identically. Keeping the stock alias and
+            // password means an APK built here is byte-compatible with one built by a
+            // default Android toolchain on any other machine.
+            storePassword = "android"
+            keyAlias = "androiddebugkey"
+            keyPassword = "android"
+        }
+    }
+
     buildTypes {
         debug {
             enableUnitTestCoverage = true
diff --git a/keystore/listen-debug.keystore b/keystore/listen-debug.keystore
new file mode 100644
index 0000000..c2b34ce
--- /dev/null
+++ b/keystore/listen-debug.keystore