diff --git a/packages/loopover-miner/lib/replay-snapshot.ts b/packages/loopover-miner/lib/replay-snapshot.ts
index 7cdc14dc6e..363e9798f4 100644
--- a/packages/loopover-miner/lib/replay-snapshot.ts
+++ b/packages/loopover-miner/lib/replay-snapshot.ts
@@ -75,9 +75,18 @@ function normalizeRepoFullName(repoFullName: string): string {
   return `${owner}/${repo}`;
 }
 
+// A commit SHA is joined straight into REPLAY_SNAPSHOT_SUBDIR (and later passed to git as a bare revision),
+// so a value like "../../../tmp/evil" (or one containing a path separator) would escape the intended snapshot
+// directory via path.join (#7796). Constrain it to a single safe path segment -- the same restricted charset
+// repo-clone.ts's isValidRepoSegment guard uses for owner/repo (#5831), plus an explicit "."/".." rejection.
+// A genuine commit SHA is hex and always satisfies this, so no legitimate caller regresses.
+const COMMIT_SHA_PATTERN = /^[A-Za-z0-9._-]+$/;
+
 function normalizeCommitSha(commitSha: string): string {
   if (typeof commitSha !== "string" || !commitSha.trim()) throw new Error("invalid_commit_sha");
-  return commitSha.trim();
+  const trimmed = commitSha.trim();
+  if (trimmed === "." || trimmed === ".." || !COMMIT_SHA_PATTERN.test(trimmed)) throw new Error("invalid_commit_sha");
+  return trimmed;
 }
 
 /** Worktree exports live under this dir inside the repo, mirroring worktree-allocator.ts's WORKTREE_SUBDIR. */
diff --git a/test/unit/miner-replay-snapshot.test.ts b/test/unit/miner-replay-snapshot.test.ts
index f1ef84628c..31a0c1cf11 100644
--- a/test/unit/miner-replay-snapshot.test.ts
+++ b/test/unit/miner-replay-snapshot.test.ts
@@ -3,7 +3,12 @@ import { tmpdir } from "node:os";
 import { join } from "node:path";
 import { afterEach, describe, expect, it, vi } from "vitest";
 
-import {
+// Import the .ts SOURCE (not the build-time .js) via a non-literal specifier. The committed lib is .ts-only,
+// but once `build:miner` has produced the artifact, a plain `.js`/extensionless import loads that .js, leaving
+// coverage.include's `.ts` entry at 0% -- that .js-vs-.ts mismatch is why this file's new guard kept reporting
+// 0% patch coverage. A variable specifier loads (and instruments) the .ts while dodging TS5097 (#7796).
+const REPLAY_SNAPSHOT_MODULE = "../../packages/loopover-miner/lib/replay-snapshot.ts";
+const {
   closeDefaultReplaySnapshotStore,
   exportReplaySnapshot,
   openReplaySnapshotStore,
@@ -11,7 +16,7 @@ import {
   removeReplaySnapshotWorktree,
   REPLAY_SNAPSHOT_SUBDIR,
   validateSnapshotFreshness,
-} from "../../packages/loopover-miner/lib/replay-snapshot.js";
+} = (await import(REPLAY_SNAPSHOT_MODULE)) as typeof import("../../packages/loopover-miner/lib/replay-snapshot.js");
 
 const FIELD_SEP = "\x1f";
 
@@ -77,6 +82,20 @@ describe("planReplaySnapshotPath (#3010) — pure, deterministic", () => {
     expect(planReplaySnapshotPath({ repoPath: "/repo", commitSha: "abc123" })).toBe(a);
     expect(planReplaySnapshotPath({ repoPath: "/repo", commitSha: "def456" })).not.toBe(a);
   });
+
+  it("rejects a commit SHA that would escape the snapshot subdir via path traversal or a separator (#7796)", () => {
+    // Without the guard, join()ing these into REPLAY_SNAPSHOT_SUBDIR escapes the repo entirely (e.g.
+    // ".../../../../../tmp/evil"). Each must be rejected up front rather than producing an out-of-sandbox path.
+    for (const commitSha of ["../../../../tmp/evil", "..", ".", "a/b", "a\\b", "../abc123", "foo/../..", " ../x "]) {
+      expect(() => planReplaySnapshotPath({ repoPath: "/repo", commitSha })).toThrow("invalid_commit_sha");
+    }
+  });
+
+  it("still confines a genuine hex commit SHA to the snapshot subdir (#7796)", () => {
+    const sha = "0a1b2c3d4e5f60718293a4b5c6d7e8f901234567";
+    const p = planReplaySnapshotPath({ repoPath: "/repo", commitSha: `  ${sha}  ` }).replaceAll("\\", "/");
+    expect(p).toBe(`/repo/${REPLAY_SNAPSHOT_SUBDIR}/${sha}`);
+  });
 });
 
 describe("validateSnapshotFreshness (#3010) — pure fail-fast check", () => {