Track a general spec.coding-agent-lab.md variant-spec convention

.gitignore

@@ -1,14 +1,19 @@
 # Built apps are artifacts; never tracked anywhere in this repo.
 builds/
 
-# Course folders are tracked, but only the spec and the source materials
-# ship: courses/<name>/spec.md and courses/<name>/materials/. Everything
-# else per course (builds/, evals/, scratch) stays local. Ignoring at
-# depth two (courses/*/*) instead of courses/* lets the negations work —
-# git can't re-include files whose parent directory is ignored.
+# Course folders are tracked, but only the canonical spec, an optional
+# variant spec, and the source materials ship: courses/<name>/spec.md,
+# courses/<name>/spec.coding-agent-lab.md, and courses/<name>/materials/.
+# The variant file is a tracked exploration copy of the canonical spec
+# (e.g. testing a Decision Ledger change) — same name across every course,
+# so this one negation covers all of them without a per-experiment edit.
+# Everything else per course (builds/, evals/, scratch) stays local.
+# Ignoring at depth two (courses/*/*) instead of courses/* lets the
+# negations work — git can't re-include files whose parent directory is ignored.
 courses/*/*
 !courses/*/spec.md
 !courses/*/materials/
+!courses/*/spec.coding-agent-lab.md
 
 # Personal scratch file — kept on disk, not version-controlled.
 notes.md

CLAUDE.md

@@ -131,9 +131,13 @@ would leak course content into the docs themselves.
 - `evals/run-NN/` is generated to match the build. The run number is the join key
   between a build and its evaluation — keep them aligned. Evals require an explicit
   `run-NN`; if none is given, list the runs in `builds/` and ask — never default.
-- **Version control:** per course, only `spec.md` and `materials/` are tracked.
-  Everything else under `courses/<name>/` — `builds/`, `evals/`, scratch — is
-  gitignored and stays local to the machine that ran the build.
+- **Version control:** per course, only `spec.md`, `materials/`, and an optional
+  `spec.coding-agent-lab.md` are tracked. The latter is a variant of the canonical
+  spec for exploring a Decision Ledger change (e.g. removing an Options entry)
+  without touching `spec.md` itself — same filename across every course, so it
+  needs no per-experiment `.gitignore` edit. Everything else under
+  `courses/<name>/` — `builds/`, `evals/`, scratch — is gitignored and stays
+  local to the machine that ran the build.
 
 ## Run numbering
 `run-NN` is per course (`run-01`, `run-02`, …). Every new build is a new run —

README.md

@@ -196,6 +196,8 @@ against the spec it was actually built from, not a spec you regenerated later.
   on demand. There is no `Stop` hook, no `.active-run` pointer, no
   `build-complete` marker — `evals/run-NN/.session` is a write-once breadcrumb
   recording which transcript to slice.
-- Per course, only `spec.md` and `materials/` are version-controlled. Everything
-  else under `courses/<name>/` — `builds/` (built apps are artifacts) and
-  `evals/` — is gitignored and stays local.
+- Per course, only `spec.md`, `materials/`, and an optional
+  `spec.coding-agent-lab.md` (a tracked variant of the canonical spec, for
+  exploring a Decision Ledger change without touching `spec.md`) are
+  version-controlled. Everything else under `courses/<name>/` — `builds/`
+  (built apps are artifacts) and `evals/` — is gitignored and stays local.