A Rebuild on every component, and the keystore AGP actually uses

Two things, both from the same stuck download.

Each component row now carries its own Rebuild, which is /build scoped to
it -- the route already took ?component=, only the button was missing.
Update builds only what the staleness rules call behind, and those rules
cannot see a command reading undeclared files, an output changed
underneath this server, or a signing key replaced since the APK was made;
in all of those Update does nothing and the only force was a project-wide
Rebuild that rebuilds every sibling. Same action at two scales, so it
takes the project Rebuild's word and colour. hasBuild is new on the
manifest component so a component with no command of its own draws none,
which the project-level needsBuild could not answer.

And debug_keystore_path() now resolves the preferences directory the way
AGP does instead of assuming ~/.android: ANDROID_USER_HOME as-is, then
ANDROID_PREFS_ROOT and ANDROID_SDK_HOME with .android appended, then
$XDG_CONFIG_HOME/.android when that directory exists, then $HOME/.android.
Measured by running real builds against AGP 32.3.2, including the
existence test on the XDG step, which the documentation does not mention.
An ordinary desktop machine with XDG_CONFIG_HOME set signs its APKs with
a keystore this server never looked at, so it reported "no debug
keystore" about a machine that had one and was using it -- and this VM
sets no XDG_CONFIG_HOME, which is why it could not happen here. The
failure now names a keystore found further down the list, since an inert
one and an absent one are otherwise identical from a phone.

Verified on the emulator (component Rebuild: press, that component's own
progress, back to resting with no sibling moving) and against a
throwaway server for both keystore branches.

Reported by the tdep-survey session, which found the two keystores on the
serving host.

Co-Authored-By: Claude Opus 5 <noreply@anthropic.com>

AGENTS.md

@@ -255,6 +255,23 @@ mutable at runtime from the phone.
   that silence. It is part of the acceptance gate like every other
   declared field -- `same_declaration` destructures exhaustively, which is
   what forced the decision when the field was added.
+- **The debug keystore is not `~/.android/debug.keystore`** -- that is the
+  last of five places, and `sdk::android_prefs_dirs` resolves it the way
+  AGP does, because the only thing that makes it the right key is being
+  the file Gradle signed with. Measured against AGP 32.3.2 by running real
+  builds: `$ANDROID_USER_HOME` is the preferences directory itself with no
+  `.android` under it, `$ANDROID_PREFS_ROOT` and `$ANDROID_SDK_HOME` get
+  `.android` appended, then `$XDG_CONFIG_HOME/.android` **but only when
+  that directory already exists** (the bytecode tests it and falls
+  through), then `$HOME/.android`. That fourth step is the whole bug: an
+  ordinary desktop Linux machine with `XDG_CONFIG_HOME` set signs its APKs
+  with a keystore this server never looked at, so it reported "no debug
+  keystore" about a machine that had one and was using it -- and this VM
+  sets no `XDG_CONFIG_HOME`, which is why the case could not appear here.
+  The failure names a keystore found further down the list, because an
+  inert one and an absent one look identical from a phone: mistaking one
+  for the other is what turned "this machine has none" into a signature
+  mismatch nobody could explain.
 - **A stripped copy is only serveable if it is signed by the key the
   build was.** `strip.rs` re-signs with `~/.android/debug.keystore`, and
   nothing about a debug keystore says which builds it made -- it is per
@@ -633,10 +650,28 @@ mutable at runtime from the phone.
   `BuildState::{trigger_if_needed,build_now,run_build,is_stale}` all take
   the same `Option<&str>` -- `None` still means the whole project, which
   is what `Pull & Build`, the project-row `Rebuild`, and every project
-  with a single component keep doing. There is deliberately no
-  component-scoped Rebuild: forcing one component's build without
-  touching the rest happens by pressing Update on it, which runs
-  `/prepare` scoped to that component.
+  with a single component keep doing. **Each component's row carries its
+  own Rebuild**, which is `/build` scoped to it. That used to be
+  deliberately absent, on the grounds that Update already builds a
+  component that needs it -- but Update runs `/prepare`, which builds only
+  when the staleness rules say the output is behind, and those rules are
+  blind to everything a commit does not describe: a command reading files
+  nobody declared, an output changed underneath this server, a signing key
+  replaced since the APK was made. In all of them nothing reads as stale,
+  so Update does nothing, and the only force was a project-wide Rebuild
+  that rebuilds every sibling too. Iris asked for the per-component
+  button on 2026-09-01. The two are the same action at two scales, so
+  they share a word and a colour, and each sits at the right-hand end of
+  its own row.
+  A component with no command of its own draws no Rebuild -- `hasBuild`
+  on the manifest component says so per component, which the project's
+  own `needsBuild` (the OR of every component's) cannot. Absent rather
+  than disabled, matching the project row, because having no build step
+  is not a state a component is in.
+  A server's Rebuild sits in its service row but outside the condition
+  that draws the service buttons: those wait for the script's answer,
+  while a server whose script cannot be reached is still one this machine
+  can compile.
   **Where `component.dir()` belongs is now one definition**
   (`Component::dir` in `config.rs`), because a second one very nearly
   shipped a real bug: `component_is_stale`'s "never built at all" check