diff --git a/lib/analyze-action-post.js b/lib/analyze-action-post.js
index 904a09bb1..87ce60ef1 100644
--- a/lib/analyze-action-post.js
+++ b/lib/analyze-action-post.js
@@ -162327,10 +162327,19 @@ function computeChangedFiles(baseFileOids, overlayFileOids) {
 }
 async function getDiffRangeFilePaths(sourceRoot, logger) {
   const jsonFilePath = getDiffRangesJsonFilePath();
+  if (!fs2.existsSync(jsonFilePath)) {
+    logger.debug(
+      `No diff ranges JSON file found at ${jsonFilePath}; skipping.`
+    );
+    return [];
+  }
   let contents;
   try {
     contents = await fs2.promises.readFile(jsonFilePath, "utf8");
-  } catch {
+  } catch (e) {
+    logger.warning(
+      `Failed to read diff ranges JSON file at ${jsonFilePath}: ${e}`
+    );
     return [];
   }
   let diffRanges;
@@ -162347,6 +162356,11 @@ async function getDiffRangeFilePaths(sourceRoot, logger) {
   );
   const repoRoot = await getGitRoot(sourceRoot);
   if (repoRoot === void 0) {
+    if (getOptionalInput("source-root")) {
+      throw new Error(
+        "Cannot determine git root to convert diff range paths relative to source-root. Failing to avoid omitting files from the analysis."
+      );
+    }
     logger.warning(
       "Cannot determine git root; returning diff range paths as-is."
     );
diff --git a/lib/analyze-action.js b/lib/analyze-action.js
index a665a6ef9..7a3c36e44 100644
--- a/lib/analyze-action.js
+++ b/lib/analyze-action.js
@@ -107922,10 +107922,19 @@ function computeChangedFiles(baseFileOids, overlayFileOids) {
 }
 async function getDiffRangeFilePaths(sourceRoot, logger) {
   const jsonFilePath = getDiffRangesJsonFilePath();
+  if (!fs3.existsSync(jsonFilePath)) {
+    logger.debug(
+      `No diff ranges JSON file found at ${jsonFilePath}; skipping.`
+    );
+    return [];
+  }
   let contents;
   try {
     contents = await fs3.promises.readFile(jsonFilePath, "utf8");
-  } catch {
+  } catch (e) {
+    logger.warning(
+      `Failed to read diff ranges JSON file at ${jsonFilePath}: ${e}`
+    );
     return [];
   }
   let diffRanges;
@@ -107942,6 +107951,11 @@ async function getDiffRangeFilePaths(sourceRoot, logger) {
   );
   const repoRoot = await getGitRoot(sourceRoot);
   if (repoRoot === void 0) {
+    if (getOptionalInput("source-root")) {
+      throw new Error(
+        "Cannot determine git root to convert diff range paths relative to source-root. Failing to avoid omitting files from the analysis."
+      );
+    }
     logger.warning(
       "Cannot determine git root; returning diff range paths as-is."
     );
diff --git a/lib/autobuild-action.js b/lib/autobuild-action.js
index 0017ab87a..8d22f4268 100644
--- a/lib/autobuild-action.js
+++ b/lib/autobuild-action.js
@@ -104381,10 +104381,19 @@ function computeChangedFiles(baseFileOids, overlayFileOids) {
 }
 async function getDiffRangeFilePaths(sourceRoot, logger) {
   const jsonFilePath = getDiffRangesJsonFilePath();
+  if (!fs2.existsSync(jsonFilePath)) {
+    logger.debug(
+      `No diff ranges JSON file found at ${jsonFilePath}; skipping.`
+    );
+    return [];
+  }
   let contents;
   try {
     contents = await fs2.promises.readFile(jsonFilePath, "utf8");
-  } catch {
+  } catch (e) {
+    logger.warning(
+      `Failed to read diff ranges JSON file at ${jsonFilePath}: ${e}`
+    );
     return [];
   }
   let diffRanges;
@@ -104401,6 +104410,11 @@ async function getDiffRangeFilePaths(sourceRoot, logger) {
   );
   const repoRoot = await getGitRoot(sourceRoot);
   if (repoRoot === void 0) {
+    if (getOptionalInput("source-root")) {
+      throw new Error(
+        "Cannot determine git root to convert diff range paths relative to source-root. Failing to avoid omitting files from the analysis."
+      );
+    }
     logger.warning(
       "Cannot determine git root; returning diff range paths as-is."
     );
diff --git a/lib/init-action-post.js b/lib/init-action-post.js
index 55c74ea00..8ec12eb27 100644
--- a/lib/init-action-post.js
+++ b/lib/init-action-post.js
@@ -165839,10 +165839,19 @@ function computeChangedFiles(baseFileOids, overlayFileOids) {
 }
 async function getDiffRangeFilePaths(sourceRoot, logger) {
   const jsonFilePath = getDiffRangesJsonFilePath();
+  if (!fs3.existsSync(jsonFilePath)) {
+    logger.debug(
+      `No diff ranges JSON file found at ${jsonFilePath}; skipping.`
+    );
+    return [];
+  }
   let contents;
   try {
     contents = await fs3.promises.readFile(jsonFilePath, "utf8");
-  } catch {
+  } catch (e) {
+    logger.warning(
+      `Failed to read diff ranges JSON file at ${jsonFilePath}: ${e}`
+    );
     return [];
   }
   let diffRanges;
@@ -165859,6 +165868,11 @@ async function getDiffRangeFilePaths(sourceRoot, logger) {
   );
   const repoRoot = await getGitRoot(sourceRoot);
   if (repoRoot === void 0) {
+    if (getOptionalInput("source-root")) {
+      throw new Error(
+        "Cannot determine git root to convert diff range paths relative to source-root. Failing to avoid omitting files from the analysis."
+      );
+    }
     logger.warning(
       "Cannot determine git root; returning diff range paths as-is."
     );
diff --git a/lib/init-action.js b/lib/init-action.js
index 76ef8f9f6..4d03be3ee 100644
--- a/lib/init-action.js
+++ b/lib/init-action.js
@@ -105491,10 +105491,19 @@ function computeChangedFiles(baseFileOids, overlayFileOids) {
 }
 async function getDiffRangeFilePaths(sourceRoot, logger) {
   const jsonFilePath = getDiffRangesJsonFilePath();
+  if (!fs3.existsSync(jsonFilePath)) {
+    logger.debug(
+      `No diff ranges JSON file found at ${jsonFilePath}; skipping.`
+    );
+    return [];
+  }
   let contents;
   try {
     contents = await fs3.promises.readFile(jsonFilePath, "utf8");
-  } catch {
+  } catch (e) {
+    logger.warning(
+      `Failed to read diff ranges JSON file at ${jsonFilePath}: ${e}`
+    );
     return [];
   }
   let diffRanges;
@@ -105511,6 +105520,11 @@ async function getDiffRangeFilePaths(sourceRoot, logger) {
   );
   const repoRoot = await getGitRoot(sourceRoot);
   if (repoRoot === void 0) {
+    if (getOptionalInput("source-root")) {
+      throw new Error(
+        "Cannot determine git root to convert diff range paths relative to source-root. Failing to avoid omitting files from the analysis."
+      );
+    }
     logger.warning(
       "Cannot determine git root; returning diff range paths as-is."
     );
@@ -110588,8 +110602,8 @@ async function loadRepositoryProperties(repositoryNwo, logger) {
   }
 }
 async function computeAndPersistDiffRanges(codeql, features, logger) {
-  try {
-    await withGroupAsync("Compute PR diff ranges", async () => {
+  await withGroupAsync("Computing PR diff ranges", async () => {
+    try {
       const branches = await getDiffInformedAnalysisBranches(
         codeql,
         features,
@@ -110607,12 +110621,12 @@ async function computeAndPersistDiffRanges(codeql, features, logger) {
       logger.info(
         `Persisted ${ranges.length} diff range(s) across ${distinctFiles} file(s).`
       );
-    });
-  } catch (e) {
-    logger.warning(
-      `Failed to compute and persist PR diff ranges: ${getErrorMessage(e)}`
-    );
-  }
+    } catch (e) {
+      logger.warning(
+        `Failed to compute and persist PR diff ranges: ${getErrorMessage(e)}`
+      );
+    }
+  });
 }
 async function recordZstdAvailability(config, zstdAvailability) {
   addNoLanguageDiagnostic(
diff --git a/lib/resolve-environment-action.js b/lib/resolve-environment-action.js
index cf5710a71..c55a0bb1a 100644
--- a/lib/resolve-environment-action.js
+++ b/lib/resolve-environment-action.js
@@ -104374,10 +104374,19 @@ function computeChangedFiles(baseFileOids, overlayFileOids) {
 }
 async function getDiffRangeFilePaths(sourceRoot, logger) {
   const jsonFilePath = getDiffRangesJsonFilePath();
+  if (!fs2.existsSync(jsonFilePath)) {
+    logger.debug(
+      `No diff ranges JSON file found at ${jsonFilePath}; skipping.`
+    );
+    return [];
+  }
   let contents;
   try {
     contents = await fs2.promises.readFile(jsonFilePath, "utf8");
-  } catch {
+  } catch (e) {
+    logger.warning(
+      `Failed to read diff ranges JSON file at ${jsonFilePath}: ${e}`
+    );
     return [];
   }
   let diffRanges;
@@ -104394,6 +104403,11 @@ async function getDiffRangeFilePaths(sourceRoot, logger) {
   );
   const repoRoot = await getGitRoot(sourceRoot);
   if (repoRoot === void 0) {
+    if (getOptionalInput("source-root")) {
+      throw new Error(
+        "Cannot determine git root to convert diff range paths relative to source-root. Failing to avoid omitting files from the analysis."
+      );
+    }
     logger.warning(
       "Cannot determine git root; returning diff range paths as-is."
     );
diff --git a/lib/setup-codeql-action.js b/lib/setup-codeql-action.js
index bbb235feb..8e901cda1 100644
--- a/lib/setup-codeql-action.js
+++ b/lib/setup-codeql-action.js
@@ -104265,10 +104265,19 @@ function computeChangedFiles(baseFileOids, overlayFileOids) {
 }
 async function getDiffRangeFilePaths(sourceRoot, logger) {
   const jsonFilePath = getDiffRangesJsonFilePath();
+  if (!fs3.existsSync(jsonFilePath)) {
+    logger.debug(
+      `No diff ranges JSON file found at ${jsonFilePath}; skipping.`
+    );
+    return [];
+  }
   let contents;
   try {
     contents = await fs3.promises.readFile(jsonFilePath, "utf8");
-  } catch {
+  } catch (e) {
+    logger.warning(
+      `Failed to read diff ranges JSON file at ${jsonFilePath}: ${e}`
+    );
     return [];
   }
   let diffRanges;
@@ -104285,6 +104294,11 @@ async function getDiffRangeFilePaths(sourceRoot, logger) {
   );
   const repoRoot = await getGitRoot(sourceRoot);
   if (repoRoot === void 0) {
+    if (getOptionalInput("source-root")) {
+      throw new Error(
+        "Cannot determine git root to convert diff range paths relative to source-root. Failing to avoid omitting files from the analysis."
+      );
+    }
     logger.warning(
       "Cannot determine git root; returning diff range paths as-is."
     );
diff --git a/lib/upload-lib.js b/lib/upload-lib.js
index 97be959c0..08a444719 100644
--- a/lib/upload-lib.js
+++ b/lib/upload-lib.js
@@ -107530,10 +107530,19 @@ function computeChangedFiles(baseFileOids, overlayFileOids) {
 }
 async function getDiffRangeFilePaths(sourceRoot, logger) {
   const jsonFilePath = getDiffRangesJsonFilePath();
+  if (!fs3.existsSync(jsonFilePath)) {
+    logger.debug(
+      `No diff ranges JSON file found at ${jsonFilePath}; skipping.`
+    );
+    return [];
+  }
   let contents;
   try {
     contents = await fs3.promises.readFile(jsonFilePath, "utf8");
-  } catch {
+  } catch (e) {
+    logger.warning(
+      `Failed to read diff ranges JSON file at ${jsonFilePath}: ${e}`
+    );
     return [];
   }
   let diffRanges;
@@ -107550,6 +107559,11 @@ async function getDiffRangeFilePaths(sourceRoot, logger) {
   );
   const repoRoot = await getGitRoot(sourceRoot);
   if (repoRoot === void 0) {
+    if (getOptionalInput("source-root")) {
+      throw new Error(
+        "Cannot determine git root to convert diff range paths relative to source-root. Failing to avoid omitting files from the analysis."
+      );
+    }
     logger.warning(
       "Cannot determine git root; returning diff range paths as-is."
     );
diff --git a/lib/upload-sarif-action.js b/lib/upload-sarif-action.js
index 6b6d24bfe..808098d96 100644
--- a/lib/upload-sarif-action.js
+++ b/lib/upload-sarif-action.js
@@ -107240,10 +107240,19 @@ function computeChangedFiles(baseFileOids, overlayFileOids) {
 }
 async function getDiffRangeFilePaths(sourceRoot, logger) {
   const jsonFilePath = getDiffRangesJsonFilePath();
+  if (!fs3.existsSync(jsonFilePath)) {
+    logger.debug(
+      `No diff ranges JSON file found at ${jsonFilePath}; skipping.`
+    );
+    return [];
+  }
   let contents;
   try {
     contents = await fs3.promises.readFile(jsonFilePath, "utf8");
-  } catch {
+  } catch (e) {
+    logger.warning(
+      `Failed to read diff ranges JSON file at ${jsonFilePath}: ${e}`
+    );
     return [];
   }
   let diffRanges;
@@ -107260,6 +107269,11 @@ async function getDiffRangeFilePaths(sourceRoot, logger) {
   );
   const repoRoot = await getGitRoot(sourceRoot);
   if (repoRoot === void 0) {
+    if (getOptionalInput("source-root")) {
+      throw new Error(
+        "Cannot determine git root to convert diff range paths relative to source-root. Failing to avoid omitting files from the analysis."
+      );
+    }
     logger.warning(
       "Cannot determine git root; returning diff range paths as-is."
     );
diff --git a/src/init-action.ts b/src/init-action.ts
index 2dddc888a..b06903d5c 100644
--- a/src/init-action.ts
+++ b/src/init-action.ts
@@ -849,8 +849,8 @@ async function computeAndPersistDiffRanges(
   features: FeatureEnablement,
   logger: Logger,
 ): Promise<void> {
-  try {
-    await withGroupAsync("Compute PR diff ranges", async () => {
+  await withGroupAsync("Computing PR diff ranges", async () => {
+    try {
       const branches = await getDiffInformedAnalysisBranches(
         codeql,
         features,
@@ -868,12 +868,12 @@ async function computeAndPersistDiffRanges(
       logger.info(
         `Persisted ${ranges.length} diff range(s) across ${distinctFiles} file(s).`,
       );
-    });
-  } catch (e) {
-    logger.warning(
-      `Failed to compute and persist PR diff ranges: ${getErrorMessage(e)}`,
-    );
-  }
+    } catch (e) {
+      logger.warning(
+        `Failed to compute and persist PR diff ranges: ${getErrorMessage(e)}`,
+      );
+    }
+  });
 }
 async function recordZstdAvailability(
   config: configUtils.Config,
diff --git a/src/overlay/index.ts b/src/overlay/index.ts
index 6c1074e55..4905b254f 100644
--- a/src/overlay/index.ts
+++ b/src/overlay/index.ts
@@ -5,6 +5,7 @@ import * as actionsCache from "@actions/cache";
 
 import * as actionsUtil from "../actions-util";
 import {
+  getOptionalInput,
   getRequiredInput,
   getTemporaryDirectory,
   getWorkflowRunAttempt,
@@ -178,10 +179,20 @@ async function getDiffRangeFilePaths(
 ): Promise<string[]> {
   const jsonFilePath = actionsUtil.getDiffRangesJsonFilePath();
 
+  if (!fs.existsSync(jsonFilePath)) {
+    logger.debug(
+      `No diff ranges JSON file found at ${jsonFilePath}; skipping.`,
+    );
+    return [];
+  }
+
   let contents: string;
   try {
     contents = await fs.promises.readFile(jsonFilePath, "utf8");
-  } catch {
+  } catch (e) {
+    logger.warning(
+      `Failed to read diff ranges JSON file at ${jsonFilePath}: ${e}`,
+    );
     return [];
   }
 
@@ -203,6 +214,12 @@ async function getDiffRangeFilePaths(
   // getFileOidsUnderPath output). Convert and filter accordingly.
   const repoRoot = await getGitRoot(sourceRoot);
   if (repoRoot === undefined) {
+    if (getOptionalInput("source-root")) {
+      throw new Error(
+        "Cannot determine git root to convert diff range paths relative to source-root. " +
+          "Failing to avoid omitting files from the analysis.",
+      );
+    }
     logger.warning(
       "Cannot determine git root; returning diff range paths as-is.",
     );