fix(agent-runtime): format POSIX scratch directory paths with forward slashes

[Totopo27]

Summary

Normalizes scratch directory path representations in system prompt guidance and Bash tool descriptions when operating under a POSIX shell dialect (including Git Bash on Windows).

Motivation & Root Cause

Resolves issue #1108 (partially addressing the Windows path behavior in Bash).

When Git Bash (dialect: "posix") is configured on Windows, the runtime emitted the raw Windows scratch path with backslashes into the system prompt and tool descriptions. In a POSIX shell context, backslashes act as escape characters rather than directory separators, breaking commands that reference the advertised scratch directory.

Key Changes

1. Dialect-Aware Scratch Path Formatting (packages/agent-runtime/src/runtime.ts):

   • Introduced formatScratchDirForShell(shell, scratchDir) to convert backslashes to forward slashes when shell.dialect === "posix".
   • Updated commandShellGuidance, commandShellToolDescription, and scratch directory prompt sections to use formatScratchDirForShell.
   • Retained native Windows backslash paths for powershell and cmd dialects.

2. Regression Testing (packages/agent-runtime/src/runtime.test.ts):

   • Added unit test formats scratch directory with forward slashes for POSIX shells verifying that Git Bash receives forward-slash normalized scratch paths in both system prompt and tool descriptions.

Verification

• Unit test suite passes cleanly: runtime.test.ts.
• Compliance with R6.1 (fix: change addressing verified upstream issue [Agent Harness] 明确 Bash 超时、编码与 Windows 路径行为 #1108).

[vastsa]

Reviewed the implementation and the targeted runtime regression. The POSIX shell path normalization is scoped to the shell dialect, preserves PowerShell/cmd paths, and covers both system guidance and Bash tool descriptions.

Validation: runtime.test.ts 257/257 passed on the PR head before the base update; after updating the branch with latest main, required JS, Rust, base, and Vercel checks all pass.