A component can name the files its build reads elsewhere

Freshness compared the commits under a component's own cwd, which is
right about where its files are and wrong about what its build reads.
tdep-survey's two clients each source one shared scripts/android-sdk-env.sh:
a fix committed there changed what every build does, moved no component's
subtree head, rebuilt nothing, and left every card correctly reporting
"current" while answering a narrower question than the reader was asking.

alsoWatch names the rest. The paths join the component's own in the same
subtree-head and dirty comparisons -- git takes several pathspecs, so it
stays one call each -- and it is part of the acceptance gate like any
other declared field. Declared rather than inferred: which files a build
reads is not knowable from here, and both wrong guesses are expensive.

Raised by the tdep-survey session, which traced why its dioxus client
could never become stale on the serving host.

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

README.md

@@ -261,6 +261,36 @@ either against source, which is what makes it cheap and needs no knowledge
 of what the build reads. The consequence is that it only means anything
 once `olderThan` has itself been built at least once.
 
+### Files a build reads from somewhere else
+
+A component is considered out of date when the commits under its own
+directory move past the ones it was built from — `cwd`, or the project
+root for a component that names none. That is right about where a
+component's *files* are and wrong about what its build *reads*: a project
+whose clients each source one shared script, which locates their SDK and
+their signing key, has a file that changes what every build does and moves
+no component's directory. A commit to it rebuilds nothing, and every card
+correctly reports "current" while answering a narrower question than you
+were asking.
+
+A component can name the rest of what it reads:
+
+```ron
+Apk(
+    name: "app",
+    cwd: "app-dioxus",
+    build: "./build-android-arm.sh",
+    alsoWatch: ["scripts"],
+),
+```
+
+Those paths join its own in the same comparison — a commit touching any of
+them is a commit to this component, and an uncommitted change in one makes
+its freshness unknown, exactly as one in its own directory does. Declared
+rather than worked out, because which files a build reads is not something
+this server can know: guess too wide and every commit rebuilds everything,
+too narrow and you are back to the silence above.
+
 Paths are relative to `projectPath` (absolute ones are also accepted), and
 `build` is argv, run without a shell — written either as a line you would
 type or as explicit arguments; the string form splits on whitespace and