[Bug] expandPath in path-utils.ts produces mixed path separators on Windows (same pattern as #1442)

[RelaxJonh]

Affected area

Coding agent — packages/coding-agent/src/core/tools/path-utils.ts

What happened?

expandPath() in path-utils.ts (line 45) has the same mixed-separator bug as #1442 (expandTildePath in config.ts):

export function expandPath(filePath: string): string {
    const normalized = normalizeUnicodeSpaces(normalizeAtPrefix(filePath));
    if (normalized === "~") {
        return os.homedir();
    }
    if (normalized.startsWith("~/")) {
        return os.homedir() + normalized.slice(1);  // BUG: string concat
    }
    return normalized;
}

On Windows, os.homedir() returns C:\Users\username (backslashes) and normalized.slice(1) returns /Documents (forward slash from the tilde path). The concatenation produces C:\Users\username/Documents — mixed separators.

Comparison with correct implementations

The same repo has correct implementations using path.join:

• extensions/loader.ts:93: path.join(os.homedir(), normalized.slice(2)) ✓
• prompt-templates.ts:193: join(homedir(), trimmed.slice(2)) ✓

Steps to reproduce

1. On Windows, set a config path to ~/some/path
2. expandPath("~/some/path") returns C:\Users\user/some/path
3. Downstream code comparing paths or using path.resolve may fail

Suggested fix

  if (normalized.startsWith("~/")) {
-     return os.homedir() + normalized.slice(1);
+     return path.join(os.homedir(), normalized.slice(1));
  }

This is the same fix pattern as #1442 for config.ts:expandTildePath.

Environment

• Prime Agent v0.8.x (main branch)
• Windows (all versions)

[RelaxJonh]

Prepared a fix on my fork: https://github.com/RelaxJonh/prime-agent/tree/fix/expand-path-mixed-separators

The fix adds join to the node:path import and replaces string concatenation with path.join:

- import { isAbsolute, resolve as resolvePath } from "node:path";
+ import { isAbsolute, join, resolve as resolvePath } from "node:path";

  if (normalized.startsWith("~/")) {
-     return os.homedir() + normalized.slice(1);
+     return join(os.homedir(), normalized.slice(1));
  }

This matches the pattern already used in extensions/loader.ts and prompt-templates.ts. Happy to PR when ready.