test(shell-env): add csh/tcsh detection and buildEnvPrefix coverage

Ultraworked with [Sisyphus](https://github.com/code-yeongyu/oh-my-openagent)

Co-authored-by: Sisyphus <clio-agent@sisyphuslabs.ai>

src/shared/shell-env.test.ts

@@ -120,6 +120,39 @@ describe("shell-env", () => {
 
       expect(result).toBe("unix")
     })
+
+    test("#given SHELL set to /bin/csh #when detectShellType is called #then returns csh", () => {
+      delete process.env.PSModulePath
+      delete process.env.MSYSTEM
+      process.env.SHELL = "/bin/csh"
+      Object.defineProperty(process, "platform", { value: "linux" })
+
+      const result = detectShellType()
+
+      expect(result).toBe("csh")
+    })
+
+    test("#given SHELL set to /bin/tcsh #when detectShellType is called #then returns csh", () => {
+      delete process.env.PSModulePath
+      delete process.env.MSYSTEM
+      process.env.SHELL = "/bin/tcsh"
+      Object.defineProperty(process, "platform", { value: "linux" })
+
+      const result = detectShellType()
+
+      expect(result).toBe("csh")
+    })
+
+    test("#given SHELL set to /usr/local/bin/tcsh #when detectShellType is called #then returns csh", () => {
+      delete process.env.PSModulePath
+      delete process.env.MSYSTEM
+      process.env.SHELL = "/usr/local/bin/tcsh"
+      Object.defineProperty(process, "platform", { value: "darwin" })
+
+      const result = detectShellType()
+
+      expect(result).toBe("csh")
+    })
   })
 
   describe("shellEscape", () => {
@@ -311,5 +344,27 @@ describe("shell-env", () => {
         expect(result).toBe("")
       })
     })
+
+    describe("csh", () => {
+      test("#given single environment variable #when buildEnvPrefix is called with csh #then builds setenv command", () => {
+        const result = buildEnvPrefix({ VAR: "value" }, "csh")
+        expect(result).toBe("setenv VAR value;")
+      })
+
+      test("#given multiple environment variables #when buildEnvPrefix is called with csh #then builds separate setenv commands", () => {
+        const result = buildEnvPrefix({ VAR1: "val1", VAR2: "val2" }, "csh")
+        expect(result).toBe("setenv VAR1 val1; setenv VAR2 val2;")
+      })
+
+      test("#given env var with spaces #when buildEnvPrefix is called with csh #then escapes value with single quotes", () => {
+        const result = buildEnvPrefix({ MSG: "has spaces" }, "csh")
+        expect(result).toBe("setenv MSG 'has spaces';")
+      })
+
+      test("#given empty env object #when buildEnvPrefix is called with csh #then returns empty string", () => {
+        const result = buildEnvPrefix({}, "csh")
+        expect(result).toBe("")
+      })
+    })
   })
 })