fix: resolve Windows-style backslash paths in input resolution

[Tyagiquamar]

Problem

isResolvablePath() only treats a value as a resolvable file path when it contains a forward slash:

return value.includes("/") && value.endsWith(".md");

On Windows, absolute paths and fs.mkdtempSync-produced paths use \ separators (C:\Users\me\docs\file.md), so every such input fails the check. resolveValue() / resolveInputs() then return the literal path string to the model instead of the file's content — silently, since a Windows path looks like a perfectly valid literal.

This breaks 9 existing tests on Windows (test/press-resolver.test.ts: 8, test/rlm.test.ts "resolves .md file paths to content in system prompt": 1); they all write real temp files and pass absolute native paths through resolution. It also affects real CLI/library usage on Windows: press run ... --input C:\path\doc.md passes the path string itself into the program context instead of the document.

Provenance: found by running the test suite on Windows (no matching open issue at the time of writing).

Fix

Accept both / and \ as path separators in isResolvablePath(). All callers (resolveValue, resolveInputs, and resolveContextValue in system-prompt.ts) route through this single predicate, so one change fixes context-stack file inlining as well as caller-input resolution. POSIX behavior is unchanged; URLs remain excluded.

Also fixes one platform-naive test assertion that assumed POSIX output from path.join("a", "b"), and adds a unit case documenting backslash acceptance.

Testing

• npx vitest --run test/press-resolver.test.ts test/environment.test.ts test/rlm.test.ts
  • Before: Tests 10 failed | 176 passed (186) on Windows
  • After: Tests 117 passed (117)
• npm run build — clean compile.