diff --git a/apps/server/src/sourceControl/GitHubCli.test.ts b/apps/server/src/sourceControl/GitHubCli.test.ts
index 964ed3d021c1..a7fa162df4d5 100644
--- a/apps/server/src/sourceControl/GitHubCli.test.ts
+++ b/apps/server/src/sourceControl/GitHubCli.test.ts
@@ -292,6 +292,42 @@ describe("GitHubCli.layer", () => {
     }).pipe(Effect.provide(layer)),
   );
 
+  it.effect("maps a repository resolution failure to GitHubRepositoryNotFoundError", () =>
+    Effect.gen(function* () {
+      const exitError = VcsProcessExitError.fromProcessExit(
+        {
+          operation: "GitHubCli.execute",
+          command: "gh",
+          cwd: "/repo",
+          argumentCount: 5,
+        },
+        {
+          exitCode: 1,
+          stderr:
+            "GraphQL: Could not resolve to a Repository with the name 'octocat/nope'. (repository)",
+          stderrTruncated: false,
+        },
+        "repository-not-found",
+      );
+      assert.strictEqual(exitError.detail, "Repository not found.");
+      mockRun.mockReturnValueOnce(Effect.fail(exitError));
+
+      const gh = yield* GitHubCli.GitHubCli;
+      const error = yield* Effect.flip(
+        gh.getRepositoryCloneUrls({
+          cwd: "/repo",
+          repository: "octocat/nope",
+        }),
+      );
+
+      assert.strictEqual(error._tag, "GitHubRepositoryNotFoundError");
+      assert.strictEqual(
+        error.detail,
+        "Repository not found. Check the owner/repo path and try again.",
+      );
+    }).pipe(Effect.provide(layer)),
+  );
+
   it.effect("creates repositories and parses clone URLs from create output", () =>
     Effect.gen(function* () {
       mockRun.mockReturnValueOnce(
diff --git a/apps/server/src/sourceControl/GitHubCli.ts b/apps/server/src/sourceControl/GitHubCli.ts
index 974574cbd20e..7b28855cb16a 100644
--- a/apps/server/src/sourceControl/GitHubCli.ts
+++ b/apps/server/src/sourceControl/GitHubCli.ts
@@ -77,6 +77,19 @@ export class GitHubPullRequestNotFoundError extends Schema.TaggedErrorClass<GitH
   }
 }
 
+export class GitHubRepositoryNotFoundError extends Schema.TaggedErrorClass<GitHubRepositoryNotFoundError>()(
+  "GitHubRepositoryNotFoundError",
+  gitHubCliFailureFields,
+) {
+  get detail(): string {
+    return "Repository not found. Check the owner/repo path and try again.";
+  }
+
+  override get message(): string {
+    return `GitHub CLI failed in execute: ${this.detail}`;
+  }
+}
+
 export class GitHubCliCommandError extends Schema.TaggedErrorClass<GitHubCliCommandError>()(
   "GitHubCliCommandError",
   gitHubCliFailureFields,
@@ -153,6 +166,7 @@ export const GitHubCliError = Schema.Union([
   GitHubCliAuthenticationError,
   GitHubCliRateLimitError,
   GitHubPullRequestNotFoundError,
+  GitHubRepositoryNotFoundError,
   GitHubCliCommandError,
   GitHubPullRequestListDecodeError,
   GitHubChangeRequestListDecodeError,
@@ -190,6 +204,9 @@ export function fromVcsError(
     if (error.failureKind === "not-found") {
       return new GitHubPullRequestNotFoundError({ ...context, cause: error });
     }
+    if (error.failureKind === "repository-not-found") {
+      return new GitHubRepositoryNotFoundError({ ...context, cause: error });
+    }
   }
 
   return new GitHubCliCommandError({ ...context, cause: error });
diff --git a/apps/server/src/sourceControl/GitHubSourceControlProvider.ts b/apps/server/src/sourceControl/GitHubSourceControlProvider.ts
index 3dcc8ab826a6..6fb45cb159bc 100644
--- a/apps/server/src/sourceControl/GitHubSourceControlProvider.ts
+++ b/apps/server/src/sourceControl/GitHubSourceControlProvider.ts
@@ -253,6 +253,9 @@ export const make = Effect.gen(function* () {
                 input.repository,
               ),
               detail: error.detail,
+              // GitHubCliError details are compile-time constants, so they are
+              // safe to show the user in place of the generic fallback.
+              userDetail: error.detail,
               cause: error,
             }),
         ),
diff --git a/apps/server/src/sourceControl/GitLabCli.ts b/apps/server/src/sourceControl/GitLabCli.ts
index 9a9fc3360247..0c5cce099a88 100644
--- a/apps/server/src/sourceControl/GitLabCli.ts
+++ b/apps/server/src/sourceControl/GitLabCli.ts
@@ -142,6 +142,7 @@ export class GitLabCliCommandError extends Schema.TaggedErrorClass<GitLabCliComm
           case "rate-limited":
             return new GitLabCliRateLimitError({ ...context, cause });
           case "not-found":
+          case "repository-not-found":
           case "command-failed":
           case undefined:
             return new GitLabCliCommandError({ ...context, cause });
diff --git a/apps/server/src/sourceControl/SourceControlRepositoryService.test.ts b/apps/server/src/sourceControl/SourceControlRepositoryService.test.ts
index 861da9a10e05..d0dbe063fcf6 100644
--- a/apps/server/src/sourceControl/SourceControlRepositoryService.test.ts
+++ b/apps/server/src/sourceControl/SourceControlRepositoryService.test.ts
@@ -150,6 +150,41 @@ it.effect("preserves provider failures without deriving the repository message f
   }).pipe(Effect.provide(makeLayer({ provider })));
 });
 
+it.effect("surfaces the provider's curated user detail when one is set", () => {
+  const providerCause = new SourceControlProviderError({
+    provider: "github",
+    operation: "getRepositoryCloneUrls",
+    cwd: "/workspace",
+    repository: "octocat/nope",
+    detail: "gh stderr that stays server-side",
+    userDetail: "Repository not found. Check the owner/repo path and try again.",
+  });
+  const provider = makeProvider({
+    getRepositoryCloneUrls: () => Effect.fail(providerCause),
+  });
+
+  return Effect.gen(function* () {
+    const service = yield* SourceControlRepositoryService.SourceControlRepositoryService;
+    const error = yield* Effect.flip(
+      service.lookupRepository({
+        provider: "github",
+        repository: "octocat/nope",
+        cwd: "/workspace",
+      }),
+    );
+
+    assert.strictEqual(
+      error.detail,
+      "Repository not found. Check the owner/repo path and try again.",
+    );
+    assert.strictEqual(
+      error.message,
+      "Source control repository operation lookupRepository failed for github: Repository not found. Check the owner/repo path and try again.",
+    );
+    assert.strictEqual(error.cause, providerCause);
+  }).pipe(Effect.provide(makeLayer({ provider })));
+});
+
 it.effect("clones a looked-up repository into the requested destination", () =>
   Effect.gen(function* () {
     const fs = yield* FileSystem.FileSystem;
diff --git a/apps/server/src/sourceControl/SourceControlRepositoryService.ts b/apps/server/src/sourceControl/SourceControlRepositoryService.ts
index 1b46369e25c4..e1aae6edc969 100644
--- a/apps/server/src/sourceControl/SourceControlRepositoryService.ts
+++ b/apps/server/src/sourceControl/SourceControlRepositoryService.ts
@@ -7,6 +7,7 @@ import * as Path from "effect/Path";
 import * as Schema from "effect/Schema";
 
 import {
+  SourceControlProviderError,
   SourceControlRepositoryError,
   type SourceControlCloneRepositoryInput,
   type SourceControlCloneRepositoryResult,
@@ -23,6 +24,7 @@ import { ServerConfig } from "../config.ts";
 import * as GitVcsDriver from "../vcs/GitVcsDriver.ts";
 import * as SourceControlProviderRegistry from "./SourceControlProviderRegistry.ts";
 const isSourceControlRepositoryError = Schema.is(SourceControlRepositoryError);
+const isSourceControlProviderError = Schema.is(SourceControlProviderError);
 
 export class SourceControlRepositoryService extends Context.Service<
   SourceControlRepositoryService,
@@ -46,7 +48,12 @@ function mapRepositoryError(operation: string, provider: SourceControlProviderKi
       : new SourceControlRepositoryError({
           operation,
           provider,
-          detail: "The source control operation could not be completed.",
+          // Provider `detail` may quote provider output, so only the curated
+          // `userDetail` opt-in reaches the client; everything else stays
+          // behind the generic sentence.
+          detail:
+            (isSourceControlProviderError(cause) ? cause.userDetail : undefined) ??
+            "The source control operation could not be completed.",
           cause,
         }),
   );
diff --git a/apps/server/src/vcs/VcsProcess.test.ts b/apps/server/src/vcs/VcsProcess.test.ts
index bd3e5b4cdce2..6337c274c6b4 100644
--- a/apps/server/src/vcs/VcsProcess.test.ts
+++ b/apps/server/src/vcs/VcsProcess.test.ts
@@ -315,3 +315,26 @@ describe("VcsProcess.run", () => {
     }).pipe(provideLive),
   );
 });
+
+describe("classifyNonZeroExit", () => {
+  it("classifies a gh repository resolution failure as repository-not-found", () => {
+    expect(
+      VcsProcess.classifyNonZeroExit(
+        "gh",
+        "GraphQL: Could not resolve to a Repository with the name 'octocat/nope'. (repository)",
+      ),
+    ).toBe("repository-not-found");
+  });
+
+  it("keeps gh pull request resolution failures as not-found", () => {
+    expect(
+      VcsProcess.classifyNonZeroExit("gh", "GraphQL: Could not resolve to a PullRequest."),
+    ).toBe("not-found");
+  });
+
+  it("does not classify repository resolution failures for other commands", () => {
+    expect(VcsProcess.classifyNonZeroExit("git", "could not resolve to a repository")).toBe(
+      "command-failed",
+    );
+  });
+});
diff --git a/apps/server/src/vcs/VcsProcess.ts b/apps/server/src/vcs/VcsProcess.ts
index ec245fa13604..d52ad160dbe9 100644
--- a/apps/server/src/vcs/VcsProcess.ts
+++ b/apps/server/src/vcs/VcsProcess.ts
@@ -53,7 +53,7 @@ const DEFAULT_TIMEOUT_MS = 30_000;
 const DEFAULT_MAX_OUTPUT_BYTES = 1_000_000;
 const OUTPUT_TRUNCATED_MARKER = "\n\n[truncated]";
 
-const classifyNonZeroExit = (command: string, stderr: string): VcsProcessExitFailureKind => {
+export const classifyNonZeroExit = (command: string, stderr: string): VcsProcessExitFailureKind => {
   const normalized = stderr.toLowerCase();
 
   if (
@@ -79,6 +79,10 @@ const classifyNonZeroExit = (command: string, stderr: string): VcsProcessExitFai
     return "rate-limited";
   }
 
+  if (command === "gh" && normalized.includes("could not resolve to a repository")) {
+    return "repository-not-found";
+  }
+
   if (
     (command === "gh" &&
       (normalized.includes("could not resolve to a pullrequest") ||
diff --git a/packages/contracts/src/sourceControl.ts b/packages/contracts/src/sourceControl.ts
index 104aadd9161f..12023dfff2f2 100644
--- a/packages/contracts/src/sourceControl.ts
+++ b/packages/contracts/src/sourceControl.ts
@@ -160,6 +160,13 @@ export class SourceControlProviderError extends Schema.TaggedErrorClass<SourceCo
     repository: Schema.optional(Schema.String),
     reference: Schema.optional(Schema.String),
     detail: Schema.String,
+    /**
+     * Set only to a compile-time constant that is safe to show the user.
+     * `detail` may quote provider output and stays out of client-facing
+     * errors; `userDetail` is the adapter's explicit opt-in to surface a
+     * curated explanation instead of the generic fallback.
+     */
+    userDetail: Schema.optional(Schema.String),
     cause: Schema.optional(Schema.Defect()),
   },
 ) {
diff --git a/packages/contracts/src/vcs.ts b/packages/contracts/src/vcs.ts
index a0956e83bd5b..b63bbbabd821 100644
--- a/packages/contracts/src/vcs.ts
+++ b/packages/contracts/src/vcs.ts
@@ -76,6 +76,7 @@ export interface VcsProcessTimeoutFailure {
 export const VcsProcessExitFailureKind = Schema.Literals([
   "authentication",
   "not-found",
+  "repository-not-found",
   "rate-limited",
   "command-failed",
 ]);
@@ -137,13 +138,15 @@ export class VcsProcessExitError extends Schema.TaggedErrorClass<VcsProcessExitE
         ? "Authentication failed."
         : failureKind === "rate-limited"
           ? "API rate limit exceeded."
-          : failureKind === "not-found"
-            ? context.command === "glab"
-              ? "Merge request not found."
-              : context.command === "gh" || context.command === "az"
-                ? "Pull request not found."
-                : "VCS resource not found."
-            : "Process exited with a non-zero status.";
+          : failureKind === "repository-not-found"
+            ? "Repository not found."
+            : failureKind === "not-found"
+              ? context.command === "glab"
+                ? "Merge request not found."
+                : context.command === "gh" || context.command === "az"
+                  ? "Pull request not found."
+                  : "VCS resource not found."
+              : "Process exited with a non-zero status.";
 
     return new VcsProcessExitError({
       ...context,