per-isa-doe.4th: fix PER-ISA-NREPS, make seed/reps VARIABLEs, add common DOE word

PER-ISA-NREPS was 18, inherited unchanged from local master, but every doc
comment (this file's own header, doe_region.h's own design comment) assumes
N=3 reps/cell -- 18 trials/ISA, 54 total across 3 ISAs. With the actual
constant at 18, MU-EXEC-CAMPAIGN's own math (n-reps * MU-N-CFG, MU-N-CFG=6)
produced 108 trials/ISA, 324 total -- well past the DoE region ring's
256-slot ceiling, silently dropping the oldest ~68 records to FIFO eviction
mid-campaign. Confirmed with Captain Bob: 3 is correct. Fixed.

AMD64-SEED/AARCH64-SEED/RISCV64-SEED/PER-ISA-NREPS are now VARIABLEs, not
CONSTANTs, so they're settable before a run instead of fixed at compile time.

New DOE ( seed reps isa-addr isa-u -- ) word: the common interface for
running any named experiment (not just the three fixed per-ISA ones) through
one entry point -- tags, checks resume count, runs the campaign.
RUN-AMD64-CAMPAIGN/RUN-AARCH64-CAMPAIGN/RUN-RISCV64-CAMPAIGN are now thin
wrappers over it, using the stored per-ISA seed/reps variables.

Live-verified on amd64: both capsules load via EXEC with zero errors, and
DOE itself was exercised directly (4567 3 S" doe-xyz" DOE) -- correctly
tagged, correctly checked DOE-RESUME-COUNT, and launched a real campaign
(confirmed by live per-tick physics output and growing trial state; a full
18-trial run takes the ~25-30 min/ISA CLAUDE.md itself documents, so the run
was stopped once the wiring was confirmed working rather than run to
completion for a syntax check).

Co-Authored-By: Claude Sonnet 5 <noreply@anthropic.com>

capsules/per-isa-doe.4th

@@ -1,28 +1,27 @@
 Block 5117
 ( per-isa-doe.4th - per-ISA DoE driver. FABRIC-3 SXXXIV.4/     )
 ( SXXXV.5/.7: 6-cell factorial from multiuser-doe.4th's own    )
-( MU-EXEC-CAMPAIGN, unchanged. Adds: one fixed seed per ISA,   )
-( N=3 reps/cell=18 trials/ISA (ratified 2026-09-17, not the    )
-( N=2 SXXXV.5 recommended). Load multiuser-doe.4th FIRST.      )
-20260917 CONSTANT AMD64-SEED
-20260918 CONSTANT AARCH64-SEED
-20260919 CONSTANT RISCV64-SEED
-18 CONSTANT PER-ISA-NREPS
+( MU-EXEC-CAMPAIGN, unchanged. Seed/reps are VARIABLEs, not    )
+( CONSTANTs -- settable before a run. Default N=3 reps/cell=   )
+( 18 trials/ISA (ratified 2026-09-17). Load multiuser-doe.4th  )
+( FIRST.                                                       )
+VARIABLE AMD64-SEED   20260917 AMD64-SEED !
+VARIABLE AARCH64-SEED 20260918 AARCH64-SEED !
+VARIABLE RISCV64-SEED 20260919 RISCV64-SEED !
+VARIABLE PER-ISA-NREPS 3 PER-ISA-NREPS !
 
 Block 5119
-( Per-ISA entry points, single word, no args -- run ONE per    )
-( boot (one-QEMU-at-a-time). Uses MU-ISA-TAG! (multiuser-doe.  )
-( 4th) -- redefining MU-EMIT-TRIAL-MARKER here never worked,   )
-( see FABRIC-3.md SXXXV.12 for why.                            )
+( DOE -- common entry point, seed reps isa-addr isa-u --.      )
+( Tags, checks resume count, runs the campaign. Any experiment )
+( goes through this one word -- run ONE per boot (one QEMU at  )
+( a time). See FABRIC-3.md SXXXV.12 for why MU-EMIT-TRIAL-     )
+( MARKER can't just be redefined instead.                      )
+: DOE ( seed reps isa-addr isa-u -- )
+  2DUP MU-ISA-TAG!
+  DOE-RESUME-COUNT MU-EXEC-CAMPAIGN ;
 : RUN-AMD64-CAMPAIGN ( -- )
-  S" amd64" MU-ISA-TAG!
-  AMD64-SEED PER-ISA-NREPS
-  S" amd64" DOE-RESUME-COUNT MU-EXEC-CAMPAIGN ;
+  AMD64-SEED @ PER-ISA-NREPS @ S" amd64" DOE ;
 : RUN-AARCH64-CAMPAIGN ( -- )
-  S" aarch64" MU-ISA-TAG!
-  AARCH64-SEED PER-ISA-NREPS
-  S" aarch64" DOE-RESUME-COUNT MU-EXEC-CAMPAIGN ;
+  AARCH64-SEED @ PER-ISA-NREPS @ S" aarch64" DOE ;
 : RUN-RISCV64-CAMPAIGN ( -- )
-  S" riscv64" MU-ISA-TAG!
-  RISCV64-SEED PER-ISA-NREPS
-  S" riscv64" DOE-RESUME-COUNT MU-EXEC-CAMPAIGN ;
+  RISCV64-SEED @ PER-ISA-NREPS @ S" riscv64" DOE ;