Submit plan to get meter-speed going again.

.agents/memory/MEMORY.md

@@ -6,3 +6,4 @@ Project-shared agent memory for music21. One file per fact; see frontmatter for
 - [sortedcontainers for streams](sortedcontainers-for-streams.md) — tried twice to make streams always-sorted via SortedList; abandoned, too slow for tiny streams
 - [Stream subclass generic defaults](stream-subclass-generic-defaults.md) — how `inherit-generics` should work once PEP 696 default type params land; maybe add typing_extensions
 - [BFS-flatten-iterator](bfs-flatten-iterator.md) — lazy breadth-first flatten is writable (maybe for tree first), but must not reuse the flat/flatten name tied to offsetInHierarchy
+- [Meter immutability re-apply](meter-immutability-reapply.md) — meter-speed is too stale to merge; re-apply FrozenDuration + immutable MeterTerminal + tuple NumDenom fresh on master

.agents/memory/meter-immutability-reapply.md

@@ -0,0 +1,34 @@
+---
+name: meter-immutability-reapply
+description: Plan to re-apply the meter-speed immutability rewrite fresh on master instead of merging the stale branch
+metadata:
+  type: project
+---
+
+The `origin/meter-speed` branch (16 commits, Oct 2022) is a two-part meter rewrite:
+
+1. **Representation change** — meter's internal form goes from strings (`'1/4'`,
+   `f'1/{d}'`) to tuples: `NumDenom = tuple[int, int]` (i.e. `(1, 4)`), with
+   `NumDenomTuple` / `MeterOptions` aliases in `meter/tools.py`.
+2. **Immutability** — `MeterTerminal` / `MeterSequence` become slotted and
+   immutable (`SlottedObjectMixin` / `common.FrozenObject`, `FrozenDuration`,
+   `_durationFromNumeratorDenominator` cached with `lru_cache`). Immutable meter
+   terminals can be shared/cached with no defensive copies.
+
+**Why not just merge master in (decided 2026-06-30):** the branch is 879 commits
+behind. Merging `master` produced deep *semantic* conflicts — 31 hunks in
+`meter/core.py`, 8 in `meter/tools.py` — because master independently evolved the
+*string-based, mutable* code for a year+ (added typing like `-> None`, a `weight`
+property, parse fast-paths, and a public→private rename `addTerminal` →
+`_addTerminal`). Almost every hunk is two different implementations of the same
+method, and the str→tuple change ripples into callers. Resolving that merge would
+mean finishing+rebasing the rewrite through hundreds of collisions — not worth it.
+
+**How to apply:** treat `origin/meter-speed` as a *reference*, not a mergeable
+branch. Start a clean branch off current `master` and re-apply only the wanted
+pieces as a fresh, reviewable change: `FrozenDuration`, slotted/immutable
+`MeterTerminal` & `MeterSequence`, and the tuple `NumDenom` internal
+representation. Note `common.FrozenObject` is **already in master** (typed for
+3.12+), so only the meter-specific immutability needs porting. Validate against the
+full `music21/meter` test suite and fix downstream callers. Keep `origin/meter-speed`
+until the re-apply lands; delete it afterward.