refactor(codegen): extract blocks/scene_manifests.zig from main_zig.zig (part of #183)

[apotema]

Summary

Per the cut plan in #193 (step 5: blocks/scene_manifests.zig, low risk):

• Moved writeSceneAssetManifests and writeSceneInitialStateManifests
  out of src/main_zig.zig into src/codegen/blocks/scene_manifests.zig
  (137-line module, well under the 200-line target).
• Re-exported through main_zig.zig as pub const scene_manifests_block
  plus private function aliases so existing call sites inside the
  orchestrator stay unchanged (the pub const couldn't reuse the bare
  name scene_manifests because that's an existing function-parameter
  name elsewhere in the file — Zig forbids the shadow).
• Depends on idents.zig from refactor(codegen): extract idents helpers from main_zig.zig (#183, step 2) #195 (writeZigString, pathToIdent).

src/main_zig.zig: 3817 → 3714 lines (-103 lines net after re-exports).
src/codegen/blocks/scene_manifests.zig: 137 lines (new).

Base-branch dependency

Branched from refactor/183-extract-next (the #195 idents extraction).
Two sibling agents are simultaneously extracting validate.zig and
blocks/asset_wiring.zig from the same base; the re-export header of
main_zig.zig will need a mechanical merge at merge time (each PR adds
one pub const line).

Test plan

• zig build — clean
• zig build test — exit 0, same test count
• scripts/gen_all_examples.sh — 8/8 working examples generate (sokol_imgui soft-fails as expected without labelle-imgui sibling)
• Bit-identical generated output:
  • 9/9 main.zig files byte-identical against refactor/183-extract-next
  • 65/65 .zig files byte-identical
  • 110/110 generated non-deps files byte-identical
  • Only flow_catalog.json differs (timestamp only, as documented in the cut plan)

Refs: #183
Builds on: #195

[gemini-code-assist]

Code Review

This pull request initiates a refactoring plan to split the large src/main_zig.zig file into smaller, more modular submodules under src/codegen/. Specifically, it extracts discovery and scanning helpers into src/codegen/scan.zig, string and identifier helpers into src/codegen/idents.zig, and scene-manifest block writers into src/codegen/blocks/scene_manifests.zig, while maintaining backward compatibility via re-exports. It also introduces a verification script to ensure bit-identical output generation. The review feedback highlights two key improvements: updating pathToPascal to handle digit-leading paths by prefixing them with an underscore to avoid invalid Zig type names, and replacing std.debug.print with standard logging (std.log.err) for user-facing errors in CLI tools.

[gemini-code-assist]

The pathToPascal function does not handle cases where the first alphanumeric character of the path is a digit (e.g., 2x2_tile). In Zig, identifiers (including type names) must not start with a digit. To prevent generating invalid Zig code, prefix the generated identifier with an underscore if the first character is a digit, matching the behavior of pathToIdent and sanitizePluginIdent.

pub fn pathToPascal(name: []const u8, pascal_buf: *[128]u8) []const u8 {
    const end = if (std.mem.endsWith(u8, name, ".zig")) name.len - 4 else name.len;
    var i: usize = 0;
    var capitalize_next = true;
    var first_char = true;
    for (name[0..end]) |c| {
        switch (c) {
            'A'...'Z', 'a'...'z', '0'...'9' => {
                if (i >= pascal_buf.len) break;
                if (first_char and c >= '0' and c <= '9') {
                    pascal_buf[i] = '_';
                    i += 1;
                    if (i >= pascal_buf.len) break;
                }
                first_char = false;
                pascal_buf[i] = if (capitalize_next) std.ascii.toUpper(c) else c;
                i += 1;
                capitalize_next = false;
            },
            else => capitalize_next = true,
        }
    }
    return pascal_buf[0..i];
}

References

1. Zig identifiers must not start with a digit. When converting strings (such as file paths) to Zig identifiers, prefix the result with an underscore if the input starts with a digit to ensure the generated code is valid.

[gemini-code-assist]

In CLI tools, user-facing warnings and errors should be written to stderr or logged using standard logging facilities (such as std.log.err or std.log.warn) rather than using debug-specific print functions like std.debug.print.

            if (idx.* + bytes.len > b.len) {
                std.log.err("labelle: path too long for identifier (max {d} chars): too many escaped chars", .{b.len});
                @panic("path exceeds identifier buffer size");
            }

References

1. In CLI tools, use standard logging facilities (e.g. std.log.warn) or write to stderr for user-facing warnings, rather than using debug-specific print functions (e.g. std.debug.print).

[cursor]

PR Summary

Low Risk
Mechanical move of pure writer functions with re-exports and aliases; PR claims bit-identical generated main.zig output.

Overview
Moves scene-manifest codegen out of main_zig.zig into a new leaf module codegen/blocks/scene_manifests.zig, continuing the #183 split of main_zig.zig.

writeSceneAssetManifests and writeSceneInitialStateManifests (comptime SceneAssetManifests / SceneInitialStateManifests emission for generated main.zig) are relocated unchanged. main_zig.zig imports the block as scene_manifests_block (avoids shadowing an existing scene_manifests parameter name) and keeps private aliases so template generation still calls the same unqualified names. Logic still depends on idents / scan helpers from #195.

No intended change to generated output; orchestrator call sites in generateMainZigFromTemplate stay the same.

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