fix(launch): type a plain Orca agent line as is in tcsh and nu

In tcsh and nu, every Orca-built agent line ran through `/bin/sh '<script>'`,
so the agent was a child of sh in sh's process group. When the prompt was
pasted after the agent was ready, the paste guard read sh in front and, on a
loaded Mac, reported the prompt not delivered (4/4 live runs in tcsh).

Now only a line that needs it goes through `/bin/sh`: one over 512 bytes, with
a control byte, or with a character those shells would not read literally
(`!`, backslash, `"`, `$`, backtick). A plain line such as
`claude '--dangerously-skip-permissions'` is typed as on main, so the agent is
the shell's own job.

src/shared/startup-command-staging.test.ts

@@ -146,6 +146,38 @@ describe('stageStartupCommand', () => {
     }
   )
 
+  // Why: behind `/bin/sh` the agent is not the shell's own job, and a pasted prompt waits on that.
+  it.each([['/bin/tcsh'], ['/usr/bin/nu'], [undefined]])(
+    'types a short plain Orca-built line as is for a shell that cannot source it (%s)',
+    (shellPath) => {
+      const command = `claude '--dangerously-skip-permissions' '--model' 'claude-opus-5-5[1m]'`
+      expect(
+        stageStartupCommand({
+          command,
+          shellPath,
+          orcaBuiltLine: true,
+          platform: 'darwin',
+          directory
+        })
+      ).toEqual({ command, delivery: 'typed' })
+      expect(readdirSync(directory)).toEqual([])
+    }
+  )
+
+  it.each([[`claude 'it'\\''s'`], ['claude "x"'], ["claude '$HOME'"], ["claude 'a`b'"]])(
+    'stages a short Orca-built line tcsh would not read literally: %s',
+    (command) => {
+      const staged = stageStartupCommand({
+        command,
+        shellPath: '/bin/tcsh',
+        orcaBuiltLine: true,
+        platform: 'darwin',
+        directory
+      })
+      expect(staged.command).toBe(`/bin/sh '${staged.scriptPath}'`)
+    }
+  )
+
   it('types a short Orca-built line in a shell that reads its quoting literally', () => {
     const command = `claude 'wow!! great'`
     expect(

src/shared/startup-command-staging.ts

@@ -32,9 +32,9 @@ export type StartupCommandStaging = {
   failure?: string
 }
 
-// Why only these type a short line as is: Orca's portable quoting is verified literal in these. Any
-// other shell (tcsh, nu, xonsh, pwsh...) runs an agent launch line Orca built through `/bin/sh`
-// instead; a command the user wrote for that shell is typed as it always was.
+// Why only these type any short line as is: Orca's portable quoting is verified literal in these. Any
+// other shell (tcsh, nu, xonsh, pwsh...) runs an agent launch line Orca built through `/bin/sh` when
+// it holds anything but plain characters; a command the user wrote for that shell is typed as it was.
 const STAGING_SHELLS = new Set(['bash', 'zsh', 'sh', 'dash', 'fish', 'ksh', 'mksh'])
 
 // Why not ksh: it runs a sourced file's commands in the shell's own process group, so Ctrl-Z could
@@ -63,17 +63,15 @@ export function shouldStageStartupCommand(args: {
     return false
   }
   const shellName = stagingShellName(args.shellPath)
-  if (shellName === null) {
-    // Why every length: Orca's POSIX quoting is literal only in the shells above (tcsh doubles a
-    // quoted backslash and expands `!!`), so another shell only ever sees the script's inert path.
-    return args.orcaBuiltLine === true
-  }
   const body = stripSubmitTerminator(args.command)
-  return (
-    (hasControlByte(body) ||
-      encoder.encode(body).byteLength > TYPED_STARTUP_LINE_PROMPT_BUDGET_BYTES) &&
-    (SOURCING_SHELLS.has(shellName) || args.orcaBuiltLine === true)
-  )
+  const needsStaging =
+    hasControlByte(body) || encoder.encode(body).byteLength > TYPED_STARTUP_LINE_PROMPT_BUDGET_BYTES
+  if (shellName === null) {
+    // Why these characters: tcsh doubles a quoted backslash and expands `!!`, and nu cannot read
+    // `'\''`. A plain line is typed so the agent is the shell's own job, where the paste guard finds it.
+    return args.orcaBuiltLine === true && (needsStaging || /[!\\"`$]/.test(body))
+  }
+  return needsStaging && (SOURCING_SHELLS.has(shellName) || args.orcaBuiltLine === true)
 }
 
 function stagedScriptLine(shellName: string | null, quotedPath: string): string {