fix(scoring): pin upstream constants to the resolved SHA and fail closed on fetch failure

src/scoring/model.ts

@@ -87,15 +87,32 @@ export async function refreshScoringModelSnapshot(env: Env): Promise<ScoringMode
   const warnings: string[] = [];
   const fetchedAt = nowIso();
   const upstream = scoringUpstreamConfig(env);
-  const constantsUrl = upstreamRawUrl(upstream, "gittensor/constants.py");
-  const programmingLanguagesUrl = upstreamRawUrl(upstream, "gittensor/validator/weights/programming_languages.json");
-  const [registrySnapshot, constantsResult, languagesResult, upstreamSourceSha] = await Promise.all([
+  // Pin the fetch to the upstream ref's immutable HEAD commit SHA so a force-push / branch-rename can't silently
+  // change what every repo scores against: resolve ref → SHA first, then fetch the constants AT that SHA (an
+  // atomic SHA↔constants binding, recorded in the payload). Best-effort — if the SHA can't be resolved (a
+  // transient API error) fall back to the mutable ref so a refresh is never blocked purely on the SHA lookup.
+  const upstreamSourceSha = await fetchUpstreamRefSha(upstream, env.GITHUB_PUBLIC_TOKEN);
+  const fetchRef = upstreamSourceSha ?? upstream.ref;
+  const constantsUrl = upstreamRawUrl({ repo: upstream.repo, ref: fetchRef }, "gittensor/constants.py");
+  const programmingLanguagesUrl = upstreamRawUrl({ repo: upstream.repo, ref: fetchRef }, "gittensor/validator/weights/programming_languages.json");
+  const [registrySnapshot, constantsResult, languagesResult] = await Promise.all([
     getLatestRegistrySnapshot(env),
     fetchText(constantsUrl, env.GITHUB_PUBLIC_TOKEN),
     fetchJson(programmingLanguagesUrl, env.GITHUB_PUBLIC_TOKEN),
-    fetchUpstreamRefSha(upstream, env.GITHUB_PUBLIC_TOKEN),
   ]);
 
+  // FAIL-CLOSED (#scoring-fail-closed): a failed constants fetch must NEVER silently overwrite the last verified
+  // upstream constants with hardcoded DEFAULT_SCORING_CONSTANTS — that would move live scoring with no one
+  // noticing. Freeze the last-good snapshot instead (its age is surfaced by scoringSnapshotStalenessWarning), and
+  // only bootstrap to defaults when there is no verified last-good to fall back to.
+  if (!constantsResult.ok) {
+    const lastGood = await getLatestScoringModelSnapshot(env);
+    if (lastGood && lastGood.sourceKind !== "fallback") {
+      const frozenNote = `Upstream scoring constants refresh failed (${constantsResult.error}); froze the last-good snapshot rather than reverting to default constants.`;
+      return { ...lastGood, warnings: [...lastGood.warnings, frozenNote] };
+    }
+  }
+
   let sourceKind: ScoringModelSnapshotRecord["sourceKind"] = "raw-github";
   let constants = { ...DEFAULT_SCORING_CONSTANTS };
   let activeModelConstants: Record<string, number> = {};

test/unit/scoring.test.ts

@@ -476,6 +476,61 @@ NOVELTY_BONUS_SCALAR = 3
     expect(refreshed.sourceKind).toBe("raw-github");
   });
 
+  it("pins the constants fetch to the resolved upstream SHA (immutable) when it can be resolved", async () => {
+    const env = createTestEnv({ GITTENSOR_UPSTREAM_REPO: "custom/upstream", GITTENSOR_UPSTREAM_REF: "test" });
+    const SHA = "0123456789abcdef0123456789abcdef01234567";
+    const fetchedUrls: string[] = [];
+    vi.stubGlobal("fetch", async (input: RequestInfo | URL) => {
+      const url = input.toString();
+      fetchedUrls.push(url);
+      if (url.includes("github.com/ghapi") && url.includes("/commits/test")) return Response.json({ sha: SHA });
+      if (url.includes("constants.py")) return new Response("MERGED_PR_BASE_SCORE = 25\n");
+      if (url.includes("programming_languages.json")) return Response.json({});
+      return new Response("not found", { status: 404 });
+    });
+
+    const refreshed = await refreshScoringModelSnapshot(env);
+
+    // The constants are fetched from the immutable SHA path, not the mutable branch ref.
+    expect(refreshed.sourceUrl).toBe(`https://github.com/ghraw/custom/upstream/${SHA}/gittensor/constants.py`);
+    expect(fetchedUrls).toContain(`https://github.com/ghraw/custom/upstream/${SHA}/gittensor/constants.py`);
+    expect(fetchedUrls).not.toContain("https://github.com/ghraw/custom/upstream/test/gittensor/constants.py");
+    expect(refreshed.payload.upstreamSourceSha).toBe(SHA);
+    expect(refreshed.sourceKind).toBe("raw-github");
+  });
+
+  it("FAILS CLOSED on a failed constants fetch: freezes the last-good snapshot instead of reverting to defaults", async () => {
+    const env = createTestEnv();
+    // 1) A good refresh persists a verified raw-github snapshot.
+    vi.stubGlobal("fetch", async (input: RequestInfo | URL) => {
+      const url = input.toString();
+      if (url.includes("constants.py")) return new Response("MERGED_PR_BASE_SCORE = 25\nOSS_EMISSION_SHARE = 0.5\n");
+      if (url.includes("programming_languages.json")) return Response.json({ TypeScript: 1 });
+      return new Response("not found", { status: 404 });
+    });
+    const good = await refreshScoringModelSnapshot(env);
+    expect(good.sourceKind).toBe("raw-github");
+    expect(good.constants.OSS_EMISSION_SHARE).toBe(0.5);
+
+    // 2) Upstream now fails. Fail-closed: keep the last-good constants, do NOT revert to DEFAULT_SCORING_CONSTANTS.
+    vi.stubGlobal("fetch", async () => new Response("upstream down", { status: 500 }));
+    const frozen = await refreshScoringModelSnapshot(env);
+    expect(frozen.id).toBe(good.id); // same snapshot — froze the last-good
+    expect(frozen.sourceKind).toBe("raw-github"); // NOT "fallback"
+    expect(frozen.constants.OSS_EMISSION_SHARE).toBe(0.5); // verified upstream value, never the hardcoded default
+    expect(frozen.warnings.join(" ")).toMatch(/froze the last-good snapshot/i);
+    // No defaults snapshot was persisted — the latest is still the verified last-good.
+    await expect(getLatestScoringModelSnapshot(env)).resolves.toMatchObject({ id: good.id, sourceKind: "raw-github" });
+  });
+
+  it("bootstraps to defaults (fallback) on a failed fetch ONLY when there is no verified last-good", async () => {
+    const env = createTestEnv();
+    vi.stubGlobal("fetch", async () => new Response("missing", { status: 404 }));
+    const bootstrap = await refreshScoringModelSnapshot(env);
+    expect(bootstrap.sourceKind).toBe("fallback");
+    expect(bootstrap.warnings.join(" ")).toMatch(/fetch failed/i);
+  });
+
   it("uses saturation math as the active private preview model", () => {
     const saturationSnapshot: ScoringModelSnapshotRecord = {
       ...snapshot,