M2compiler-V1/docs/summary_step2.1.md

Step 2.1 — Image extension .MCD → .MC4 (tag: step2.1)

Commit 5c56c9f — "step2.1: rename 64-bit images .MCD -> .MC4 per spec sections 8 and 14" (57 files, pure rename + 8 one-line edits).

Rationale

The spec already mandates .MC4 (§8 file format, §14 migration row), and the tree was inconsistent (boot.mc4 vs example.MCD). The rename also disambiguates formats: legacy 16-bit inputs stay .MCD, 64-bit outputs become .MC4, so the trans8to64 flow (in.MCD → out.MC4) is self-documenting.

What changed

• Producers: mkdemo→boot.MC4, mkdtest→example.MC4, mkread→readtest.MC4, mkdep→STAK/DEP.MC4, MGen emits <Mod>.MC4, trans8to64 usage (input side kept .MCD).
• Loader2 dependency suffix, MC64.mod boot name, mcint usage text (all .MC4, uppercase per spec).
• Docs (surgical): SESSION.md, session-summary.md, spec §16 boot note. Historical .MCD mentions kept on purpose (16-bit doc, §14 migration row, translator input side).
• Tracked binaries renamed via git mv + full rebuild.

Verification after the rename

• mc64: example.MC4 24/24 exit 0, boot.MC4 → Hello, readtest.MC4 stdin echo, mcint DEP.MC4 → cross-module ok (proves the loader suffix change), mc64 → [vm end].
• m2c: 25/25, .MC4 files regenerated by the suite.