docs: tagged session summary 2026-10-19

Whole-session record (P0-P5, gap14, robustness, library): the two
root-cause corrections (ASTDUMP gate; record-array-field already fixed),
the library additions, and the final gates (suite 249/249, fixpoint OK
3,882,337 B, corpus 467/612, 0 crashes).  See
docs/summary_session-2026-10-19.md.

docs/INDEX.md

@@ -32,6 +32,8 @@ bisecting *why* a decision was made, not for reading end-to-end).
 
 ## Recent session summaries (newest first)
 
+- **`summary_session-2026-10-19.md`** — the whole 2026-10-19 session
+  (P0–P5, gap14, robustness, library; corpus 405 → 467).
 - **2026-10-19 (P0–P4):** generics double-instantiation fixed (lower each
   unit in its own scope); `__FILE__`/`__LINE__`; scalar→`ARRAY OF BYTE`;
   P2 gm2 extensions (VAR same-size, bare proc value, variant records,

docs/summary_session-2026-10-19.md

@@ -0,0 +1,111 @@
+# Session 2026-10-19 — summary
+
+Branch **`master`** (tree clean).  Eleven commits, tagged individually
+(`v3-generics-two-instances` … `v3-pim-io-libs`).  Plan source:
+`handoff-2026-10-18-next.md` (P0–P5) + `handoff-2026-10-19-next.md`.
+
+## Numbers
+
+| gate | session start | end |
+| --- | --- | --- |
+| suite (`compiler/run_tests.sh`) | 239/239 | **249/249** |
+| fixpoint (`bootstrap/fixpoint.sh`) | OK (3,812,771 B) | **OK (3,882,337 B)** |
+| corpus (`tools/v3-corpus/corpus.sh`) | 405/612 | **467/612, 0 crashes** |
+
+Reproduce:
+
+```sh
+cd compiler && ./build.sh && ./run_tests.sh          # 249/249
+cd .. && TMP="$PWD/.scratch/fixpoint" ./bootstrap/fixpoint.sh
+tools/v3-corpus/corpus.sh                            # 467 OK, 0 crash
+```
+
+## What landed
+
+### P0 — generics double-instantiation (real bug) — `dc3b3c8`
+One generic instantiated twice with different-family type arguments
+failed on the second.  Root cause was **Lowering**, not the formal
+binding: after `EndUnit`, `Lower` re-emitted each unit in `globScope`,
+so `MaterializeGlobals` copied the unit's types there; a generic instance
+leaked its `NodeRec` and the second instance's `POINTER TO NodeRec`
+resolved the first instance's record via `ForwardType`.
+Fix: `SymTab.EnterLowerScope`/`LeaveLowerScope` (re-emit each unit in its
+own scope), `Lower.ReenterImports` for nested-module FROM-imports.
+Regression `g_twice*` / `GTwiceProg`.
+
+### P1 — two gm2 extensions (user chose compatibility) — `a33fc7c`, `b042be3`
+- `__FILE__` / `__LINE__`: scanner allows a leading `_`; both are
+  reserved literals folded to the file-name string / line-number integer.
+- scalar actual → `ARRAY OF BYTE`: parse-time marker on the open formal;
+  a scalar is wrapped in a stack descriptor `[count=SIZE(actual)][copy]`
+  (`QbeGen.OpenScalarDesc`).  Approximate by design (writes hit the copy;
+  `BYTE` stays 32-bit) — documented in `gaps/README.md`.
+
+### P2 — structural gm2 extensions — `81b488b`
+`gap10` same-size scalar `VAR` actual; `gap11` PIM `PROC` type + bare
+proc-value statement; `gap12` variant empty arms / `ELSE` / comma labels
+/ untagged inner `CASE` / nested variant `CASE`; `gap18` set-typed `CASE`
+labels (word-wise `CmpSet`).  Corpus +16.
+
+### P3 — strict declaration order in bodies — `10e0951`
+Deferred bodies are now order-aware for this module's own **data**
+(variables/constants/types): `SymTab` declaration sequence + a window in
+`Lookup`; parser state moved so the parser obeys the rule.  Forward
+**procedure** calls stay allowed (the generated parser relies on it;
+gm2's bootstrap link rejects `FORWARD`).  Corpus −6 (intended: gm2
+`decl-order` leniencies now correctly rejected).
+
+### P4 — the "size-sensitive" miscompile — `a50fc6f` (docs)
+**Not size-sensitive, not a codegen bug.**  `ASTDUMP` dumped the AST to
+stdout; built from its own sources that dump contained the driver's
+literal `"Parsed correctly"`, and the fixpoint gate was `grep -q Parsed`
+— so the gate passed while the session reported `Incorrect source`.
+Removing the dump unmasked real errors (Lower's forward procedure calls),
+already fixed in `a3ef897`.  Also corrected the stale note about the
+record-array-field codegen bug (`38e0b54`): it is **fixed** (hybrid
+`ArrBodyItems`), covered by `t_arrrecfld`/`t_arrrecbig`/`t_nestarr`.
+
+### gap14 + P5 — `f53cdad`
+- `__BUILTIN__` / `__ATTRIBUTE__` declaration pragmas parsed and ignored
+  (`builtin.def/.mod` + 4 importers now compile).
+- `docs/INDEX.md` rewritten; 45 unreferenced historical files moved to
+  `docs/archive/` (all 69 cross-references kept valid).
+- `gap13` remainder (standard built-ins as identifiers) documented and
+  **deliberately deferred**: no corpus exemplar, and it needs a
+  contextual-keyword rewrite of `Fact`/`ArgList` (Coco/R is LL(1)); a
+  declaration-site-only measure would silently bind calls to the
+  built-in.
+
+### Robustness — `3d58325`
+Table-limit overflows are now loud (`230`), not silent drops: the
+two-phase span table (used to silently drop a body's codegen — regression
+`t_manyproc`), the label/`GOTO` tables, the 32-actual AST buffer, and
+`SymTab.MaxTypes`.  Corpus unchanged (no corpus file hits a limit).
+
+### Library — `c7d5cff`, `d243d25`
+- ISO 10514-1 `ChanConsts` + `StreamFile` on `IOChan`; PIM/gm2
+  `NumberIO`, `RealInOut`, `FpuIO` (new shim `m2writefix`).
+- Two real compiler bugs surfaced and fixed: **cross-unit set `CONST`s**
+  (emitted under the global name now) and **qualified enum literals in
+  set constants** (`Lower.EvalOrdConst`).
+- Harness fidelity: `corpus.sh` now resolves V3's own shipped libraries
+  by default (`V3_LIBS`), instead of mislabelling their imports `LIB`.
+
+## Corrections / lessons
+
+- The "size-sensitive miscompile" and the "still-open record-array-field
+  bug" were both stale notes; both are resolved.  Verify old findings
+  before acting on them.
+- A weak success gate (`grep -q Parsed`) can mask real errors — the gate
+  now greps `Parsed correctly` and fails on session errors.
+
+## Remaining (for a next session)
+
+1. **Corpus `LANG` bucket** — after the library work: `undeclared
+   identifier` (gm2-only modules `M2RTS`/`Builtins`/`Processes`/… aside),
+   `not supported yet`, `invalid call`.  Triage the top kinds.
+2. **Error recovery / message polish** — dropped tokens cascade.
+3. **`gap13` refactor** (optional, no corpus exemplar).
+4. `STATUS.md` "what remains" is the live list.
+
+Nothing was pushed; `origin/master` is the previous commit.