fix: better validate for dev_brain and 50k reminder not triggering rebuild

src/dev_brain.rs

@@ -72,12 +72,13 @@ sources:
   - project: Registered project name
     path: src/example.rs
     symbol: optional_symbol
-    revision: exact-clean-git-revision
-    # Use hash instead of revision when the worktree is dirty or is not Git.
+    revision: full-or-unique-short-clean-git-revision
+    # Use `git rev-parse HEAD`, or a unique lowercase hex prefix of at least 7 characters.
+    # Use hash instead when the worktree is dirty or is not Git.
 ---
 ```
 
-Each source has exactly one evidence version: `revision` or a lowercase SHA-256 `hash`. Paths are project-relative and may not escape the registered project.
+Each source has exactly one evidence version: `revision` or a lowercase SHA-256 `hash`. A revision is the current clean commit's full object ID or a unique lowercase hexadecimal prefix of at least 7 characters. Paths are project-relative and may not escape the registered project.
 
 ## Compilation
 
@@ -1081,9 +1082,9 @@ fn validate_source(source: &SourceRecord, projects: &[RegisteredProject]) -> Res
         ));
     }
     if let Some(revision) = &source.revision {
-        return Ok(
-            git_state(&project.root).is_some_and(|(current, clean)| clean && current == *revision)
-        );
+        return Ok(git_state(&project.root).is_some_and(|(current, clean)| {
+            clean && git_revision_matches(&project.root, revision, &current)
+        }));
     }
     let expected = source.hash.as_deref().unwrap();
     if expected.len() != 64
@@ -1100,6 +1101,29 @@ fn validate_source(source: &SourceRecord, projects: &[RegisteredProject]) -> Res
         && !git_state(&project.root).is_some_and(|(_, clean)| clean))
 }
 
+fn git_revision_matches(root: &Path, revision: &str, current: &str) -> bool {
+    if revision == current {
+        return true;
+    }
+    if revision.len() < 7
+        || revision.len() >= current.len()
+        || !revision
+            .bytes()
+            .all(|byte| byte.is_ascii_digit() || (b'a'..=b'f').contains(&byte))
+    {
+        return false;
+    }
+    Command::new("git")
+        .args(["-C"])
+        .arg(root)
+        .args(["rev-parse", "--verify"])
+        .arg(format!("{revision}^{{commit}}"))
+        .output()
+        .ok()
+        .filter(|output| output.status.success())
+        .is_some_and(|output| String::from_utf8_lossy(&output.stdout).trim() == current)
+}
+
 fn git_state(root: &Path) -> Option<(String, bool)> {
     let revision = Command::new("git")
         .args(["-C"])
@@ -1560,7 +1584,7 @@ mod tests {
     }
 
     #[test]
-    fn clean_git_revisions_become_stale_when_the_worktree_changes() {
+    fn clean_full_and_short_git_revisions_become_stale_when_the_worktree_changes() {
         let fixture = Fixture::new();
         for arguments in [
             vec!["init"],
@@ -1586,11 +1610,21 @@ mod tests {
             );
         }
         let revision = git_state(&fixture.project).unwrap().0;
+        assert!(git_revision_matches(
+            &fixture.project,
+            &revision[..7],
+            &revision
+        ));
+        assert!(!git_revision_matches(
+            &fixture.project,
+            &revision[..6],
+            &revision
+        ));
         let topic = fixture
             .topic("verified", &"0".repeat(64), "Revision-backed knowledge.")
             .replace(
                 &format!("hash: {}", "0".repeat(64)),
-                &format!("revision: {revision}"),
+                &format!("revision: {}", &revision[..7]),
             );
         let mut brain = fixture.brain();
         write_topic(&fixture, &mut brain, &topic).unwrap();