diff --git a/packages/opencode/src/snapshot/index.ts b/packages/opencode/src/snapshot/index.ts
index 4da9bc3ca864..f7b2e5608466 100644
--- a/packages/opencode/src/snapshot/index.ts
+++ b/packages/opencode/src/snapshot/index.ts
@@ -92,7 +92,10 @@ const layer: Layer.Layer<Service, never, FSUtil.Service | AppProcess.Service | C
           },
           Effect.catch((err) =>
             Effect.succeed({
-              code: ChildProcessSpawner.ExitCode(1),
+              // -1 is a sentinel for "git failed to run at all". Callers that give
+              // exit code 1 a meaning (check-ignore: "none ignored") must not see
+              // spawn failures as code 1, otherwise fail-closed paths get bypassed.
+              code: ChildProcessSpawner.ExitCode(-1),
               text: "",
               stderr: err instanceof Error ? err.message : String(err),
             }),
@@ -120,7 +123,16 @@ const layer: Layer.Layer<Service, never, FSUtil.Service | AppProcess.Service | C
               stdin: encodeNulTerminatedPaths(checkIgnorePaths),
             },
           )
-          if (check.code !== 0 && check.code !== 1) return new Set<string>()
+          // git check-ignore: 0 = some ignored, 1 = none ignored; any other code is an error.
+          // Fail closed: treat every candidate as ignored so gitignored files cannot leak into
+          // snapshot patches and later be restored or deleted by /undo (see #28033).
+          if (check.code !== 0 && check.code !== 1) {
+            yield* Effect.logWarning("git check-ignore failed; treating all candidates as ignored", {
+              code: check.code,
+              stderr: check.stderr,
+            })
+            return new Set(files)
+          }
           return new Set(
             check.text
               .split("\0")