009 cross module mock

// Cross-module mocking × EFFECT BRANCHES (FRONTIERS gap 5 — CLOSED 2026-06-12).
// The consumer below handles `! line` from std/fs:read-lines (effect shape).
// The REAL path streams effects as handler CALLS during the proc (650_001 is
// green end-to-end); the MOCK path substitutes a plain terminal Output value,
// so the effect branch never fires. Both now emit correctly: a result-dispatch
// switch is over TERMINALS only, and emitContinuationList drops effect (`!`)
// continuations before building it (mirrors the inline path's effect/terminal
// partition). Before the fix the mock path leaked `.line =>` against an Output
// union with no such tag and Zig rejected it.
//
// Test: Cross-module mocking
//
// This test verifies mocking events from IMPORTED modules.
//
// The syntax `~std/fs:read-lines = failed "mock error"` means:
// "For this test, provide this implementation for the std/fs:read-lines event"
//
// This is NOT just for testing - Source blocks with impl declarations enable:
// - Compile-time code synthesis
// - AI-generated implementations
// - Remote code fetching
// - Interactive compilation
//
// The compiler becomes a development partner, not just a batch processor.

~import std/testing
~import std/fs

// A flow that depends on an external module event
~event process-config { path: []const u8 }
| ok usize
| failed []const u8

~process-config = std/fs:read-lines(path)
! line _ |> _
| done n => ok n
| failed msg => failed msg

// ============================================
// THE TEST - Cross-module mock
// ============================================

~test(Cross-module mock with failed branch) {
    // Mock the external module's event with the 'failed' branch
    // This returns a simple string ([]const u8), which works without array literals
    ~std/fs:read-lines => failed "mocked file read error"

    ~process-config(path: "/this/file/does/not/exist.txt")
    | ok _ |> assert.fail()
    | failed result |> assert(result.len > 0)
}

// ============================================
// Terminal mock against the effect contract
// ============================================

~test(Cross-module mock should return 3 lines) {
    ~std/fs:read-lines => done 3

    ~process-config(path: "/fake/path")
    | ok result |> assert(result == 3)
    | failed |> assert.fail()
}