diff --git a/packages/source-control-azure-devops/src/server/AzureDevOpsCli.test.ts b/packages/source-control-azure-devops/src/server/AzureDevOpsCli.test.ts
index 3cb69661997b6..9b40406093155 100644
--- a/packages/source-control-azure-devops/src/server/AzureDevOpsCli.test.ts
+++ b/packages/source-control-azure-devops/src/server/AzureDevOpsCli.test.ts
@@ -233,6 +233,38 @@ describe("AzureDevOpsCli.layer", () => {
     }).pipe(Effect.provide(layer)),
   );
 
+  it.effect("percent-encodes the source branch while preserving recognized ref prefixes", () =>
+    Effect.gen(function* () {
+      mockRun.mockReturnValueOnce(Effect.succeed(processOutput("[]")));
+
+      const az = yield* AzureDevOpsCli.AzureDevOpsCli;
+      yield* az.listPullRequests({
+        cwd: "/somewhere",
+        headSelector: "user/feat/1-(#2)-slug",
+        state: "open",
+      });
+
+      const args = mockRun.mock.calls.at(-1)?.[0].args ?? [];
+      assert.strictEqual(args[args.indexOf("--source-branch") + 1], "user%2Ffeat%2F1-(%232)-slug");
+
+      for (const prefix of ["refs/heads/", "refs/pull/", "refs/tags/"]) {
+        mockRun.mockReturnValueOnce(Effect.succeed(processOutput("[]")));
+        yield* az.listPullRequests({
+          cwd: "/somewhere",
+          headSelector: "fallback",
+          source: { refName: `${prefix}user/feat/1-(#2)-slug` },
+          state: "open",
+        });
+
+        const refArgs = mockRun.mock.calls.at(-1)?.[0].args ?? [];
+        assert.strictEqual(
+          refArgs[refArgs.indexOf("--source-branch") + 1],
+          `${prefix}user%2Ffeat%2F1-(%232)-slug`,
+        );
+      }
+    }).pipe(Effect.provide(layer)),
+  );
+
   it.effect("preserves VCS causes without copying upstream details into messages", () =>
     Effect.gen(function* () {
       const cause = new VcsProcessExitError({
diff --git a/packages/source-control-azure-devops/src/server/AzureDevOpsCli.ts b/packages/source-control-azure-devops/src/server/AzureDevOpsCli.ts
index 57b9f4086cdaa..eb6151d336263 100644
--- a/packages/source-control-azure-devops/src/server/AzureDevOpsCli.ts
+++ b/packages/source-control-azure-devops/src/server/AzureDevOpsCli.ts
@@ -401,6 +401,11 @@ export const make = Effect.gen(function* () {
   return AzureDevOpsCli.of({
     execute,
     listPullRequests: Effect.fn("AzureDevOpsCli.listPullRequests")(function (input) {
+      const branch = SourceControlProvider.sourceBranch(input);
+      // az checks literal ref prefixes before constructing the request URL.
+      const refPrefix =
+        ["refs/heads/", "refs/pull/", "refs/tags/"].find((prefix) => branch.startsWith(prefix)) ??
+        "";
       return executeJson({
         cwd: input.cwd,
         args: [
@@ -410,7 +415,8 @@ export const make = Effect.gen(function* () {
           "--detect",
           "true",
           "--source-branch",
-          SourceControlProvider.sourceBranch(input),
+          // az puts this in the query string unescaped; a `#` would cut the request.
+          refPrefix + encodeURIComponent(branch.slice(refPrefix.length)),
           "--status",
           toAzureStatus(input.state),
           "--top",
diff --git a/packages/source-control-azure-devops/src/server/AzureDevOpsPullRequestCli.test.ts b/packages/source-control-azure-devops/src/server/AzureDevOpsPullRequestCli.test.ts
index 4b2e46b5a1e93..9bbe1468f8f54 100644
--- a/packages/source-control-azure-devops/src/server/AzureDevOpsPullRequestCli.test.ts
+++ b/packages/source-control-azure-devops/src/server/AzureDevOpsPullRequestCli.test.ts
@@ -850,6 +850,22 @@ layer("AzureDevOpsPullRequestCli.layer", (it) => {
     }),
   );
 
+  it.effect("escapes characters in a file path that would cut the query string", () =>
+    Effect.gen(function* () {
+      mockedExecute.mockReturnValueOnce(Effect.succeed(output(json({ content: "x" }))));
+      const cli = yield* AzureDevOpsPullRequestCli.AzureDevOpsPullRequestCli;
+
+      yield* cli.readItemContent({
+        cwd: "/w",
+        location: { project: "platform", repository: "web" },
+        path: "docs/C#/a&b.md",
+        commit: "a".repeat(40),
+      });
+
+      expect(mockedExecute.mock.calls.at(-1)?.[0].args).toContain("path=%2Fdocs%2FC%23%2Fa%26b.md");
+    }),
+  );
+
   it.effect("reports a pull request it cannot place as its own outcome", () =>
     Effect.gen(function* () {
       mockedExecute.mockReturnValueOnce(
diff --git a/packages/source-control-azure-devops/src/server/AzureDevOpsPullRequestCli.ts b/packages/source-control-azure-devops/src/server/AzureDevOpsPullRequestCli.ts
index 07d9c2a2057e7..81c9b2e68fb6e 100644
--- a/packages/source-control-azure-devops/src/server/AzureDevOpsPullRequestCli.ts
+++ b/packages/source-control-azure-devops/src/server/AzureDevOpsPullRequestCli.ts
@@ -603,7 +603,8 @@ export const make = Effect.gen(function* () {
         resource: "items",
         routeParameters: repositoryRoute(input.location),
         queryParameters: [
-          `path=${toItemPath(input.path)}`,
+          // `az devops invoke` does not escape query values, so `#` or `&` in a path would truncate it.
+          `path=${encodeURIComponent(toItemPath(input.path))}`,
           "versionDescriptor.versionType=commit",
           `versionDescriptor.version=${input.commit}`,
           "includeContent=true",