docs(recon): memllib usage inventory — the §7.5 prerequisite, with a wrinkle

Plan §5 names an inventory of the load-bearing memllib surface as the
prerequisite for the vendor-vs-fork-pin decision. Built it from the firmware
LINKER MAP rather than grep — the same method that would have caught daisysp
(S8) mechanically instead of by reading.

Result: all 24 compiled translation units contribute kept sections to the image;
no discarded-only TU exists. memllib is not a daisysp situation. "The
load-bearing subset" is ~1.8 MB across 84 files — essentially all of memllib
minus examples/. There is no small subset to lift; synth/ alone is 1.3 MB and
all three of its TUs link.

The wrinkle, which was not visible when §7.5 was decided: src/memllib is not a
third-party dependency, it is the LAB's shared library
(MusicallyEmbodiedML/memllib), and our fork is 3 commits ahead but 31 commits
BEHIND — +2034/-153 across exactly the files we link, including "new staticmlp",
"jolts", "noise", "verb". Vendoring as-is freezes that gap permanently.

Recommendation recorded: rebase the three small NISPS commits onto upstream main
FIRST, then vendor. Same self-contained end state, but it does not silently
discard work that sounds directly relevant, and it is the only moment that merge
is cheap — after vendoring there is no upstream history to merge against.

Flagged for an operator call before the PlatformIO cut, which this gates.

docs/specs/plans/simplification-plan.md

@@ -100,7 +100,15 @@ DESCRIPTIVE — it documents that engine voice spaces already square the value i
 One cut, no dual path. `firmware/useq-celium/` already proves the PIO + arduino-pico pattern in-repo.
 
 - `platformio.ini` with one `[env]` per firmware variant passing `-DMEMLNAUT_MODE_TYPE=<alias>`; selftest becomes a plain `-DNISPS_SELFTEST=1` env. Deletes: the sed/python machinery in `firmware-common.sh` that **mutates the committed .ino**, the `.ino` comment-registry, the entire `NISPS_ST_*` token-paste table (already silently missing the currently-active SLPWorkshop variant — L12), the sketch-tree symlink forest, and the global TFT_eSPI library mutation (handled via PIO lib config/build flags instead).
-- **memllib consumption decision** (§7.5, depends on Phase 0.1): PIO `lib_deps` pin on the fork vs vendoring the actually-used subset. Prerequisite task: inventory which memllib surface (AudioDriver, MEMLNaut board, display/menu, MIDI) is load-bearing.
+- **memllib consumption decision** (§7.5): the prerequisite inventory is DONE —
+  `../recon/memllib-usage-inventory.md`, built from the firmware linker map rather than grep. Result:
+  all 24 compiled TUs are linked, so "the load-bearing subset" is ~1.8 MB / 84 files — essentially
+  all of memllib minus `examples/`. There is no small subset to lift. It also surfaced a
+  consequence that was not visible when §7.5 was decided: memllib is the LAB's shared library and
+  our fork is 3 commits ahead but **31 behind** (+2034/−153 across the files we link, including
+  `new staticmlp`, `jolts`, `verb`). Vendoring freezes that gap permanently. Recommended: rebase the
+  three NISPS commits onto upstream `main` first, THEN vendor — it is the only moment that merge is
+  cheap. Operator call before the cut.
 - Then **S9**: a CI job compiling 2–3 representative envs with cached toolchain — firmware enters an automated gate for the first time.
 
 ## §6 Phase 5 — Vision-facing architecture (each item spec-first, own session)

docs/specs/recon/memllib-usage-inventory.md

@@ -0,0 +1,84 @@
+---
+kind: finding
+date: 2026-07-21
+---
+
+# memllib usage inventory — the prerequisite for the §7.5 ownership decision
+
+_Prerequisite named by `../plans/simplification-plan.md` §5: "inventory which memllib surface
+(AudioDriver, MEMLNaut board, display/menu, MIDI) is load-bearing" before choosing between a
+fork-pin and vendoring. The operator's §7.5 decision is **vendor the parts we use** ("everything
+should be self contained in this repo"). This document is the evidence that decision needs, plus one
+consequence that was not visible when it was made._
+
+## Method
+
+Not grep. The firmware was built for real (`arduino-cli`, `rp2040:rp2040:solderparty_rp2350_stamp_xl`,
+SLPWorkshop variant) and the **linker map** was read: `MEMLNaut-NISPS.ino.map` distinguishes
+translation units that merely compiled from those contributing sections to the final image. This is
+the same method that would have caught the daisysp finding (S8) mechanically instead of by reading.
+
+## Result: the compile surface is 24 TUs, and all 24 are linked
+
+| subdir | .cpp linked / present | headers | size |
+|---|---|---|---|
+| `audio/` | 4 / 4 | 12 | 132K |
+| `hardware/` | 7 / 7 | 21 | 176K |
+| `interface/` | 8 / 8 | 8 | 108K |
+| `synth/` | 3 / 3 | 10 | 1.3M |
+| `utils/` | 2 / 2 | 9 | 80K |
+| **total** | **24 / 24** | **60** | **~1.8M** |
+
+Every translation unit reachable through the sketch-tree symlinks contributes kept sections to the
+image — **no discarded-only TU exists**. memllib is therefore *not* a daisysp situation (41 .cpp
+compiled, zero consumers). It is genuinely load-bearing.
+
+The library has 30 `.cpp` in total; the 6 not counted above live outside the five symlinked subdirs
+(e.g. `examples/`) and are never compiled by the firmware build. Those are the only part safe to
+drop outright.
+
+Firmware's direct include surface is just six entry points — `audio/AudioDriver.hpp`,
+`hardware/memlnaut/MEMLNaut.hpp`, `hardware/memlnaut/Pins.hpp`,
+`hardware/memlnaut/display/{View,SingleSelectView}.hpp`, `interface/MIDIInOut.hpp`, `PicoDefs.hpp`,
+`utils/perf.hpp` — but the transitive closure is the whole of those five subdirs.
+
+**Consequence for vendoring: "the load-bearing subset" is ~1.8 MB / 84 files, i.e. essentially all
+of memllib minus `examples/`.** There is no small subset to lift. `synth/` alone is 1.3 MB (mostly
+`maximilian.cpp`) and all three of its TUs link.
+
+## The consequence that was not visible when §7.5 was decided
+
+`src/memllib` is not a third-party dependency. It is **the lab's shared library**
+(`MusicallyEmbodiedML/memllib`), and our fork is:
+
+- **3 commits ahead** — `bf9691c` (swap memlp includes for nisps/core, inline RL utilities),
+  `32cc831` (newlib RNG fix), `b37fc53` (seed-helper rename). These are the NISPS-specific changes.
+- **31 commits behind** — including `770a990 new staticmlp`, `9fcd459 jolts`, `d0d8a72 noise`,
+  `616b8e7 cc select`, `a8bf255 verb`, `671abbe screen ordering`, `e291192 l r input swap`.
+  Diffed against the five subdirs we link: **30 files changed, +2034 / −153**.
+
+Vendoring freezes that gap permanently and converts "we are behind the lab" into "we have our own
+divergent copy". That may be exactly what is wanted — self-containment is a real goal, and the lab's
+`main` is not obviously a branch we track — but it is a fork of a colleague-shared library, not a
+snapshot of a vendor drop, and the 31 commits contain work (`staticmlp`, `jolts`) that sounds
+directly relevant to this project.
+
+## Options, with what each costs
+
+1. **Vendor as decided.** Copy the five subdirs into the repo, drop the submodule and the symlink
+   forest, delete `examples/`. Repo grows ~1.8 MB. Self-contained, no submodule init, PlatformIO
+   gets a plain `lib/` — this materially simplifies the §5 migration. Cost: the 31 upstream commits
+   become a manual merge, forever.
+2. **Vendor, but first rebase our 3 commits onto upstream `main`.** Same end state, except the
+   snapshot is current rather than 31 commits stale. Costs one merge now (the three commits are
+   small and mechanical), and it is the only moment when that merge is cheap.
+3. **Fork-pin (status quo + Phase 0's fix).** Already works: the pin is reachable, CI is green,
+   fresh clones build. Not self-contained, and keeps the submodule friction PlatformIO would rather
+   not have.
+
+**Recommendation: option 2.** The operator's goal (self-contained) is satisfied identically by 1 and
+2, but 2 does not silently discard `staticmlp`/`jolts`/`verb`. Doing the rebase after vendoring
+means doing it against a copy that no longer has upstream history — i.e. never.
+
+This decision gates the PlatformIO migration (plan §5), which otherwise has to keep the submodule
+and its symlink workaround.