fix(app): handle Windows paths in frontend file URL encoding (#12601)

2 files changed, 222 insertions, 2 deletions

diff --git a/packages/app/src/components/prompt-input/build-request-parts.test.ts b/packages/app/src/components/prompt-input/build-request-parts.test.ts
index b284c3884..b0fd3a050 100644
--- a/packages/app/src/components/prompt-input/build-request-parts.test.ts
+++ b/packages/app/src/components/prompt-input/build-request-parts.test.ts
@@ -64,4 +64,214 @@ describe("buildRequestParts", () => {
     expect(fooFiles).toHaveLength(2)
     expect(synthetic).toHaveLength(1)
   })
+
+  test("handles Windows paths correctly (simulated on macOS)", () => {
+    const prompt: Prompt = [{ type: "file", path: "src\\foo.ts", content: "@src\\foo.ts", start: 0, end: 11 }]
+
+    const result = buildRequestParts({
+      prompt,
+      context: [],
+      images: [],
+      text: "@src\\foo.ts",
+      messageID: "msg_win_1",
+      sessionID: "ses_win_1",
+      sessionDirectory: "D:\\projects\\myapp", // Windows path
+    })
+
+    // Should create valid file URLs
+    const filePart = result.requestParts.find((part) => part.type === "file")
+    expect(filePart).toBeDefined()
+    if (filePart?.type === "file") {
+      // URL should be parseable
+      expect(() => new URL(filePart.url)).not.toThrow()
+      // Should not have encoded backslashes in wrong place
+      expect(filePart.url).not.toContain("%5C")
+      // Should have normalized to forward slashes
+      expect(filePart.url).toContain("/src/foo.ts")
+    }
+  })
+
+  test("handles Windows absolute path with special characters", () => {
+    const prompt: Prompt = [{ type: "file", path: "file#name.txt", content: "@file#name.txt", start: 0, end: 14 }]
+
+    const result = buildRequestParts({
+      prompt,
+      context: [],
+      images: [],
+      text: "@file#name.txt",
+      messageID: "msg_win_2",
+      sessionID: "ses_win_2",
+      sessionDirectory: "C:\\Users\\test\\Documents", // Windows path
+    })
+
+    const filePart = result.requestParts.find((part) => part.type === "file")
+    expect(filePart).toBeDefined()
+    if (filePart?.type === "file") {
+      // URL should be parseable
+      expect(() => new URL(filePart.url)).not.toThrow()
+      // Special chars should be encoded
+      expect(filePart.url).toContain("file%23name.txt")
+      // Should have Windows drive letter properly encoded
+      expect(filePart.url).toMatch(/file:\/\/\/[A-Z]%3A/)
+    }
+  })
+
+  test("handles Linux absolute paths correctly", () => {
+    const prompt: Prompt = [{ type: "file", path: "src/app.ts", content: "@src/app.ts", start: 0, end: 10 }]
+
+    const result = buildRequestParts({
+      prompt,
+      context: [],
+      images: [],
+      text: "@src/app.ts",
+      messageID: "msg_linux_1",
+      sessionID: "ses_linux_1",
+      sessionDirectory: "/home/user/project",
+    })
+
+    const filePart = result.requestParts.find((part) => part.type === "file")
+    expect(filePart).toBeDefined()
+    if (filePart?.type === "file") {
+      // URL should be parseable
+      expect(() => new URL(filePart.url)).not.toThrow()
+      // Should be a normal Unix path
+      expect(filePart.url).toBe("file:///home/user/project/src/app.ts")
+    }
+  })
+
+  test("handles macOS paths correctly", () => {
+    const prompt: Prompt = [{ type: "file", path: "README.md", content: "@README.md", start: 0, end: 9 }]
+
+    const result = buildRequestParts({
+      prompt,
+      context: [],
+      images: [],
+      text: "@README.md",
+      messageID: "msg_mac_1",
+      sessionID: "ses_mac_1",
+      sessionDirectory: "/Users/kelvin/Projects/opencode",
+    })
+
+    const filePart = result.requestParts.find((part) => part.type === "file")
+    expect(filePart).toBeDefined()
+    if (filePart?.type === "file") {
+      // URL should be parseable
+      expect(() => new URL(filePart.url)).not.toThrow()
+      // Should be a normal Unix path
+      expect(filePart.url).toBe("file:///Users/kelvin/Projects/opencode/README.md")
+    }
+  })
+
+  test("handles context files with Windows paths", () => {
+    const prompt: Prompt = []
+
+    const result = buildRequestParts({
+      prompt,
+      context: [
+        { key: "ctx:1", type: "file", path: "src\\utils\\helper.ts" },
+        { key: "ctx:2", type: "file", path: "test\\unit.test.ts", comment: "check tests" },
+      ],
+      images: [],
+      text: "test",
+      messageID: "msg_win_ctx",
+      sessionID: "ses_win_ctx",
+      sessionDirectory: "D:\\workspace\\app",
+    })
+
+    const fileParts = result.requestParts.filter((part) => part.type === "file")
+    expect(fileParts).toHaveLength(2)
+
+    // All file URLs should be valid
+    fileParts.forEach((part) => {
+      if (part.type === "file") {
+        expect(() => new URL(part.url)).not.toThrow()
+        expect(part.url).not.toContain("%5C") // No encoded backslashes
+      }
+    })
+  })
+
+  test("handles absolute Windows paths (user manually specifies full path)", () => {
+    const prompt: Prompt = [
+      { type: "file", path: "D:\\other\\project\\file.ts", content: "@D:\\other\\project\\file.ts", start: 0, end: 25 },
+    ]
+
+    const result = buildRequestParts({
+      prompt,
+      context: [],
+      images: [],
+      text: "@D:\\other\\project\\file.ts",
+      messageID: "msg_abs",
+      sessionID: "ses_abs",
+      sessionDirectory: "C:\\current\\project",
+    })
+
+    const filePart = result.requestParts.find((part) => part.type === "file")
+    expect(filePart).toBeDefined()
+    if (filePart?.type === "file") {
+      // Should handle absolute path that differs from sessionDirectory
+      expect(() => new URL(filePart.url)).not.toThrow()
+      expect(filePart.url).toContain("/D%3A/other/project/file.ts")
+    }
+  })
+
+  test("handles selection with query parameters on Windows", () => {
+    const prompt: Prompt = [
+      {
+        type: "file",
+        path: "src\\App.tsx",
+        content: "@src\\App.tsx",
+        start: 0,
+        end: 11,
+        selection: { startLine: 10, startChar: 0, endLine: 20, endChar: 5 },
+      },
+    ]
+
+    const result = buildRequestParts({
+      prompt,
+      context: [],
+      images: [],
+      text: "@src\\App.tsx",
+      messageID: "msg_sel",
+      sessionID: "ses_sel",
+      sessionDirectory: "C:\\project",
+    })
+
+    const filePart = result.requestParts.find((part) => part.type === "file")
+    expect(filePart).toBeDefined()
+    if (filePart?.type === "file") {
+      // Should have query parameters
+      expect(filePart.url).toContain("?start=10&end=20")
+      // Should be valid URL
+      expect(() => new URL(filePart.url)).not.toThrow()
+      // Query params should parse correctly
+      const url = new URL(filePart.url)
+      expect(url.searchParams.get("start")).toBe("10")
+      expect(url.searchParams.get("end")).toBe("20")
+    }
+  })
+
+  test("handles file paths with dots and special segments on Windows", () => {
+    const prompt: Prompt = [
+      { type: "file", path: "..\\..\\shared\\util.ts", content: "@..\\..\\shared\\util.ts", start: 0, end: 21 },
+    ]
+
+    const result = buildRequestParts({
+      prompt,
+      context: [],
+      images: [],
+      text: "@..\\..\\shared\\util.ts",
+      messageID: "msg_dots",
+      sessionID: "ses_dots",
+      sessionDirectory: "C:\\projects\\myapp\\src",
+    })
+
+    const filePart = result.requestParts.find((part) => part.type === "file")
+    expect(filePart).toBeDefined()
+    if (filePart?.type === "file") {
+      // Should be valid URL
+      expect(() => new URL(filePart.url)).not.toThrow()
+      // Should preserve .. segments (backend normalizes)
+      expect(filePart.url).toContain("/..")
+    }
+  })
 })
diff --git a/packages/app/src/components/prompt-input/build-request-parts.ts b/packages/app/src/components/prompt-input/build-request-parts.ts
index 7010a1fd8..11aec9631 100644
--- a/packages/app/src/components/prompt-input/build-request-parts.ts
+++ b/packages/app/src/components/prompt-input/build-request-parts.ts
@@ -30,11 +30,21 @@ type BuildRequestPartsInput = {
 const absolute = (directory: string, path: string) =>
   path.startsWith("/") ? path : (directory + "/" + path).replace("//", "/")
 
-const encodeFilePath = (filepath: string): string =>
-  filepath
+const encodeFilePath = (filepath: string): string => {
+  // Normalize Windows paths: convert backslashes to forward slashes
+  let normalized = filepath.replace(/\\/g, "/")
+
+  // Handle Windows absolute paths (D:/path -> /D:/path for proper file:// URLs)
+  if (/^[A-Za-z]:/.test(normalized)) {
+    normalized = "/" + normalized
+  }
+
+  // Encode each path segment (preserving forward slashes as path separators)
+  return normalized
     .split("/")
     .map((segment) => encodeURIComponent(segment))
     .join("/")
+}
 
 const fileQuery = (selection: FileSelection | undefined) =>
   selection ? `?start=${selection.startLine}&end=${selection.endLine}` : ""