fix(source-control): compare check run timestamps by instant

packages/source-control-core/src/server/pullRequestChecks.test.ts

@@ -20,6 +20,40 @@ function entry(
 }
 
 describe("dedupeChecks", () => {
+  it.each([
+    ["2026-10-16T12:00:00Z", "2026-10-16T12:00:00.500Z"],
+    ["2026-10-16T12:00:00+02:00", "2026-10-16T10:30:00Z"],
+    ["2026-10-16T12:00:00.0001Z", "2026-10-16T12:00:00.0002Z"],
+    ["2026-10-16T12:00:00.0001z", "2026-10-16T12:00:00.0002z"],
+    ["2026-10-16T12:00:00.00009Z", "2026-10-16T12:00:00.0001Z"],
+  ])("keeps the newer instant between %s and %s in either listing order", (older, newer) => {
+    const oldRun = entry("build", "success", { at: older });
+    const newRun = entry("build", "failure", { at: newer });
+
+    expect(
+      [
+        [oldRun, newRun],
+        [newRun, oldRun],
+      ].map((runs) => dedupeChecks(runs)[0]?.status),
+    ).toEqual(["failure", "failure"]);
+  });
+
+  it.each([
+    ["2026-10-16T12:00:00Z", "2026-10-16T12:00:00.000Z"],
+    ["2026-10-16T12:00:00Z", "2026-10-16T14:00:00+02:00"],
+  ])("takes the last copy for equal instants %s and %s", (first, second) => {
+    const forward = dedupeChecks([
+      entry("build", "success", { at: first }),
+      entry("build", "failure", { at: second }),
+    ]);
+    const reversed = dedupeChecks([
+      entry("build", "success", { at: second }),
+      entry("build", "failure", { at: first }),
+    ]);
+
+    expect([forward[0]?.status, reversed[0]?.status]).toEqual(["failure", "failure"]);
+  });
+
   it("keeps the newest run of a check the host listed twice", () => {
     const checks = dedupeChecks([
       entry("Prepare PR size config", "success", {
@@ -37,6 +71,15 @@ describe("dedupeChecks", () => {
     ]);
   });
 
+  it("preserves text ordering when a host supplies an unparseable timestamp", () => {
+    expect(
+      dedupeChecks([
+        entry("build", "success", { at: "invalid-a" }),
+        entry("build", "failure", { at: "invalid-b" }),
+      ]).map((check) => check.status),
+    ).toEqual(["failure"]);
+  });
+
   it("holds a check at the place it first appeared, so a re-run does not reshuffle the list", () => {
     const checks = dedupeChecks([
       entry("lint", "success", { workflowName: "CI", at: "2026-08-11T16:00:00Z" }),

packages/source-control-core/src/server/pullRequestChecks.ts

@@ -1,9 +1,25 @@
 import type { PullRequestCheck } from "@t3tools/contracts";
 
-/** ISO-8601 timestamps in UTC compare correctly as plain text, which is all the ordering needs. */
+// Parse whole seconds separately so sub-millisecond fractions keep their precision.
+function timestampParts(value: string) {
+  const fraction = /\.(\d+)(?=Z$|[+-]\d{2}:\d{2}$)/i.exec(value);
+  return {
+    time: Date.parse(fraction ? value.replace(fraction[0], "") : value),
+    fraction: fraction?.[1] ?? "",
+  };
+}
+
 function isAtLeastAsNew(candidate: string | null, kept: string | null): boolean {
   if (candidate === null) return kept === null;
-  return kept === null || candidate >= kept;
+  if (kept === null) return true;
+  const candidateParts = timestampParts(candidate);
+  const keptParts = timestampParts(kept);
+  if (Number.isNaN(candidateParts.time) || Number.isNaN(keptParts.time)) return candidate >= kept;
+  if (candidateParts.time !== keptParts.time) return candidateParts.time > keptParts.time;
+  const precision = Math.max(candidateParts.fraction.length, keptParts.fraction.length);
+  return (
+    candidateParts.fraction.padEnd(precision, "0") >= keptParts.fraction.padEnd(precision, "0")
+  );
 }
 
 /**

packages/source-control-forgejo/src/server/ForgejoSourceControlProvider.test.ts

@@ -123,7 +123,7 @@ it.effect("submits a Forgejo review without sending its summary in the prelimina
   );
 });
 
-it.effect("reads Forgejo checks without repository or viewer requests", () => {
+it.effect("reads the newest Forgejo checks without repository or viewer requests", () => {
   const paths: string[] = [];
   return Effect.gen(function* () {
     const provider = yield* ForgejoPullRequestProvider.make;
@@ -155,7 +155,7 @@ it.effect("reads Forgejo checks without repository or viewer requests", () => {
             "head":{"ref":"feature","sha":"head","repo":null},"base":{"ref":"main","sha":"base","repo":null},
             "created_at":"2026-09-16T00:00:00Z","updated_at":"2026-09-16T00:00:00Z","closed_at":null,"merged_at":null,"labels":[]}`
                 : input.path.endsWith("page=1")
-                  ? `[{"context":"build","status":"failure","description":null,"target_url":null,"updated_at":"2026-09-16T00:00:00Z"}]`
+                  ? `[{"context":"build","status":"failure","description":null,"target_url":null,"updated_at":"2026-09-16T00:00:00.500Z"},{"context":"build","status":"success","description":null,"target_url":null,"updated_at":"2026-09-16T00:00:00Z"}]`
                   : "[]",
             ),
           );