refactor(shell): apply code review feedback to getTerminalConfig

- Replace TerminalProfiles union with PlatformProfilesMap mapped type so
  the return type is inferred from the platform key, eliminating explicit
  type parameters at each call site and making mismatches a compile error
- Change || to ?? when falling back to empty profiles object
- Add JSDoc explaining the key constraint and inferred return type
- Add missing boolean/array non-string defaultProfileName test cases for
  macOS and Linux to match Windows coverage
- Add mutation-resistant tests for macOS and Linux that verify the typeof
  guard is load-bearing (numeric key matching a real profile entry)

Author: daewoongoh

src/utils/__tests__/shell.spec.ts

@@ -521,6 +521,34 @@ describe("Shell Detection Tests", () => {
 			expect(getShell()).toBe("/bin/zsh")
 		})
 
+		it("macOS: handles boolean defaultProfileName without TypeError", () => {
+			Object.defineProperty(process, "platform", { value: "darwin" })
+			const mockConfig = {
+				get: vi.fn((key: string) => {
+					if (key === "defaultProfile.osx") return true
+					if (key === "profiles.osx") return {}
+					return undefined
+				}),
+			}
+			vi.mocked(vscode.workspace.getConfiguration).mockReturnValue(mockConfig as any)
+
+			expect(getShell()).toBe("/bin/zsh")
+		})
+
+		it("macOS: handles array defaultProfileName without TypeError", () => {
+			Object.defineProperty(process, "platform", { value: "darwin" })
+			const mockConfig = {
+				get: vi.fn((key: string) => {
+					if (key === "defaultProfile.osx") return ["zsh"]
+					if (key === "profiles.osx") return {}
+					return undefined
+				}),
+			}
+			vi.mocked(vscode.workspace.getConfiguration).mockReturnValue(mockConfig as any)
+
+			expect(getShell()).toBe("/bin/zsh")
+		})
+
 		it("macOS: handles object defaultProfileName without TypeError", () => {
 			Object.defineProperty(process, "platform", { value: "darwin" })
 			const mockConfig = {
@@ -535,6 +563,25 @@ describe("Shell Detection Tests", () => {
 			expect(getShell()).toBe("/bin/zsh")
 		})
 
+		// Mutation-resistant: without the typeof guard, profiles[1] === profiles["1"] in JS,
+		// so a numeric key that matches a real profile would return its path instead of falling back.
+		it("macOS: ignores numeric defaultProfileName even when it matches a profile key", () => {
+			Object.defineProperty(process, "platform", { value: "darwin" })
+			const mockConfig = {
+				get: vi.fn((key: string) => {
+					if (key === "defaultProfile.osx") return 1
+					// Profile keyed as "1" — would be reached by profiles[1] if the guard were absent
+					if (key === "profiles.osx") return { "1": { path: "/usr/local/bin/zsh" } }
+					return undefined
+				}),
+			}
+			vi.mocked(vscode.workspace.getConfiguration).mockReturnValue(mockConfig as any)
+
+			// Guard treats 1 as null → getMacShellFromVSCode returns null → fallback to /bin/zsh
+			// Without the guard it would return /usr/local/bin/zsh
+			expect(getShell()).toBe("/bin/zsh")
+		})
+
 		it("Linux: handles numeric defaultProfileName without TypeError", () => {
 			Object.defineProperty(process, "platform", { value: "linux" })
 			const mockConfig = {
@@ -549,6 +596,34 @@ describe("Shell Detection Tests", () => {
 			expect(getShell()).toBe("/bin/bash")
 		})
 
+		it("Linux: handles boolean defaultProfileName without TypeError", () => {
+			Object.defineProperty(process, "platform", { value: "linux" })
+			const mockConfig = {
+				get: vi.fn((key: string) => {
+					if (key === "defaultProfile.linux") return true
+					if (key === "profiles.linux") return {}
+					return undefined
+				}),
+			}
+			vi.mocked(vscode.workspace.getConfiguration).mockReturnValue(mockConfig as any)
+
+			expect(getShell()).toBe("/bin/bash")
+		})
+
+		it("Linux: handles array defaultProfileName without TypeError", () => {
+			Object.defineProperty(process, "platform", { value: "linux" })
+			const mockConfig = {
+				get: vi.fn((key: string) => {
+					if (key === "defaultProfile.linux") return ["bash"]
+					if (key === "profiles.linux") return {}
+					return undefined
+				}),
+			}
+			vi.mocked(vscode.workspace.getConfiguration).mockReturnValue(mockConfig as any)
+
+			expect(getShell()).toBe("/bin/bash")
+		})
+
 		it("Linux: handles object defaultProfileName without TypeError", () => {
 			Object.defineProperty(process, "platform", { value: "linux" })
 			const mockConfig = {
@@ -562,6 +637,24 @@ describe("Shell Detection Tests", () => {
 
 			expect(getShell()).toBe("/bin/bash")
 		})
+
+		// Mutation-resistant: same pattern as macOS — numeric key matches profile "1" only if unguarded.
+		it("Linux: ignores numeric defaultProfileName even when it matches a profile key", () => {
+			Object.defineProperty(process, "platform", { value: "linux" })
+			const mockConfig = {
+				get: vi.fn((key: string) => {
+					if (key === "defaultProfile.linux") return 1
+					// Profile keyed as "1" — would be reached by profiles[1] if the guard were absent
+					if (key === "profiles.linux") return { "1": { path: "/usr/bin/fish" } }
+					return undefined
+				}),
+			}
+			vi.mocked(vscode.workspace.getConfiguration).mockReturnValue(mockConfig as any)
+
+			// Guard treats 1 as null → getLinuxShellFromVSCode returns null → fallback to /bin/bash
+			// Without the guard it would return /usr/bin/fish
+			expect(getShell()).toBe("/bin/bash")
+		})
 	})
 
 	// --------------------------------------------------------------------------

src/utils/shell.ts

@@ -136,19 +136,36 @@ type LinuxTerminalProfiles = Record<string, LinuxTerminalProfile>
 // 1) VS Code Terminal Configuration Helpers
 // -----------------------------------------------------
 
-type TerminalProfiles = WindowsTerminalProfiles | MacTerminalProfiles | LinuxTerminalProfiles
+type PlatformProfilesMap = {
+	windows: WindowsTerminalProfiles
+	osx: MacTerminalProfiles
+	linux: LinuxTerminalProfiles
+}
 
-function getTerminalConfig<T extends TerminalProfiles>(
-	platformKey: string,
-): { defaultProfileName: string | null; profiles: T } {
+/**
+ * Reads the VS Code terminal profile configuration for the given platform.
+ *
+ * The key must be one of `"windows"`, `"osx"`, or `"linux"` — the exact strings
+ * VS Code uses in `terminal.integrated.defaultProfile.<key>` and
+ * `terminal.integrated.profiles.<key>`. Passing any other value is a compile-time
+ * error, which prevents silent mismatches such as `"darwin"` returning empty config.
+ *
+ * The return type (`defaultProfileName` and `profiles`) is inferred from `K` via
+ * `PlatformProfilesMap`, so callers don't need an explicit type parameter.
+ *
+ * Returns `{ defaultProfileName: null, profiles: {} }` on any VS Code API error.
+ */
+function getTerminalConfig<K extends keyof PlatformProfilesMap>(
+	platformKey: K,
+): { defaultProfileName: string | null; profiles: PlatformProfilesMap[K] } {
 	try {
 		const config = vscode.workspace.getConfiguration("terminal.integrated")
 		const rawProfileName = config.get<string>(`defaultProfile.${platformKey}`)
 		const defaultProfileName = typeof rawProfileName === "string" ? rawProfileName : null
-		const profiles = config.get<T>(`profiles.${platformKey}`) || ({} as T)
+		const profiles = config.get<PlatformProfilesMap[K]>(`profiles.${platformKey}`) ?? ({} as PlatformProfilesMap[K])
 		return { defaultProfileName, profiles }
 	} catch {
-		return { defaultProfileName: null, profiles: {} as T }
+		return { defaultProfileName: null, profiles: {} as PlatformProfilesMap[K] }
 	}
 }
 
@@ -170,7 +187,7 @@ function normalizeShellPath(path: string | string[] | undefined): string | null
 
 /** Attempts to retrieve a shell path from VS Code config on Windows. */
 function getWindowsShellFromVSCode(): string | null {
-	const { defaultProfileName, profiles } = getTerminalConfig<WindowsTerminalProfiles>("windows")
+	const { defaultProfileName, profiles } = getTerminalConfig("windows")
 	if (!defaultProfileName) {
 		// No explicit Windows terminal profile is configured. VS Code auto-detects
 		// the default on modern Windows and prefers PowerShell 7 (pwsh.exe) when it
@@ -215,7 +232,7 @@ function getWindowsShellFromVSCode(): string | null {
 
 /** Attempts to retrieve a shell path from VS Code config on macOS. */
 function getMacShellFromVSCode(): string | null {
-	const { defaultProfileName, profiles } = getTerminalConfig<MacTerminalProfiles>("osx")
+	const { defaultProfileName, profiles } = getTerminalConfig("osx")
 	if (!defaultProfileName) {
 		return null
 	}
@@ -226,7 +243,7 @@ function getMacShellFromVSCode(): string | null {
 
 /** Attempts to retrieve a shell path from VS Code config on Linux. */
 function getLinuxShellFromVSCode(): string | null {
-	const { defaultProfileName, profiles } = getTerminalConfig<LinuxTerminalProfiles>("linux")
+	const { defaultProfileName, profiles } = getTerminalConfig("linux")
 	if (!defaultProfileName) {
 		return null
 	}