fix: unblock m-stdlib CI (M default + changelog path drift)

Makefile

@@ -10,8 +10,11 @@
 
 SHELL := /bin/bash
 
-# m-cli venv — Python entry point for `m fmt` / `m lint` / `m test` / `m coverage`.
-M ?= $(HOME)/projects/m-cli/.venv/bin/m
+# m-cli — Python entry point for `m fmt` / `m lint` / `m test` / `m coverage`.
+# Resolved from $PATH by default. Maintainers who keep an unactivated
+# m-cli venv can override per-shell or per-invocation, e.g.
+#   make fmt-check M=$HOME/projects/m-cli/.venv/bin/m
+M ?= m
 
 # m-test-engine — local checkout for `make engine-up` / `engine-down`.
 # Override if you cloned it elsewhere.

tools/gen-manifest.py

@@ -402,14 +402,23 @@ def build_label_entry(
 
 
 def read_stdlib_version() -> str:
-    """Read the most-recent versioned entry from CHANGELOG.md.
+    """Read the most-recent versioned entry from the changelog.
 
     Skips an `[Unreleased]` heading if present so the manifest's
     stdlib_version stays anchored to the last shipped tag while
     work accumulates against the next one.
+
+    The changelog moved in commit 90e694e from `CHANGELOG.md` at the
+    repo root to `docs/tracking/changelog.md` (per the four-bucket
+    tracking-doc model). Look at the new path first, fall back to the
+    old one for back-compat with checkouts predating that commit.
     """
-    changelog = REPO_ROOT / "CHANGELOG.md"
-    if not changelog.exists():
+    candidates = (
+        REPO_ROOT / "docs" / "tracking" / "changelog.md",
+        REPO_ROOT / "CHANGELOG.md",
+    )
+    changelog = next((p for p in candidates if p.exists()), None)
+    if changelog is None:
         return ""
     for line in changelog.read_text(encoding="utf-8").splitlines():
         m = re.match(r"^##\s*\[([^\]]+)\]", line)