add support for -w,--writable-root to add more writable roots for sandbox (#263)

This adds support for a new flag, `-w,--writable-root`, that can be
specified multiple times to _amend_ the list of folders that should be
configured as "writable roots" by the sandbox used in `full-auto` mode.
Values that are passed as relative paths will be resolved to absolute
paths.

Incidentally, this required updating a number of the `agent*.test.ts`
files: it feels like some of the setup logic across those tests could be
consolidated.

In my testing, it seems that this might be slightly out of distribution
for the model, as I had to explicitly tell it to run `apply_patch` and
that it had the permissions to write those files (initially, it just
showed me a diff and told me to apply it myself). Nevertheless, I think
this is a good starting point.

codex-cli/src/utils/agent/handle-exec-command.ts

@@ -74,6 +74,7 @@ export async function handleExecCommand(
   args: ExecInput,
   config: AppConfig,
   policy: ApprovalPolicy,
+  additionalWritableRoots: ReadonlyArray<string>,
   getCommandConfirmation: (
     command: Array<string>,
     applyPatch: ApplyPatchCommand | undefined,
@@ -91,6 +92,7 @@ export async function handleExecCommand(
       args,
       /* applyPatch */ undefined,
       /* runInSandbox */ false,
+      additionalWritableRoots,
       abortSignal,
     ).then(convertSummaryToResult);
   }
@@ -138,6 +140,7 @@ export async function handleExecCommand(
     args,
     applyPatch,
     runInSandbox,
+    additionalWritableRoots,
     abortSignal,
   );
   // If the operation was aborted in the meantime, propagate the cancellation
@@ -170,7 +173,13 @@ export async function handleExecCommand(
     } else {
       // The user has approved the command, so we will run it outside of the
       // sandbox.
-      const summary = await execCommand(args, applyPatch, false, abortSignal);
+      const summary = await execCommand(
+        args,
+        applyPatch,
+        false,
+        additionalWritableRoots,
+        abortSignal,
+      );
       return convertSummaryToResult(summary);
     }
   } else {
@@ -202,6 +211,7 @@ async function execCommand(
   execInput: ExecInput,
   applyPatchCommand: ApplyPatchCommand | undefined,
   runInSandbox: boolean,
+  additionalWritableRoots: ReadonlyArray<string>,
   abortSignal?: AbortSignal,
 ): Promise<ExecCommandSummary> {
   let { workdir } = execInput;
@@ -239,7 +249,11 @@ async function execCommand(
   const execResult =
     applyPatchCommand != null
       ? execApplyPatch(applyPatchCommand.patch)
-      : await exec(execInput, await getSandbox(runInSandbox), abortSignal);
+      : await exec(
+          { ...execInput, additionalWritableRoots },
+          await getSandbox(runInSandbox),
+          abortSignal,
+        );
   const duration = Date.now() - start;
   const { stdout, stderr, exitCode } = execResult;