FABRIC-3.md §I.2: FIRSTTOUCH + migration state machine (blk_meta_relocate_devblock)

Closes the block-subsystem punch-list item -- built exactly to §F.11's
already-decided algorithm after re-verifying it against current
blk_meta_t (a 2026-09-03 re-scoping note had wrongly claimed the chain
fields no longer existed; they do, untouched by BMAPFMT).

blk_firsttouch_claim(): one linear scan of Artemis's own device
(new blk_get_first_disk_range(), correctly bounding the scan instead of
the global multi-device LBN space), scattered-chain claim via
prev_block/next_block/chain_length, owner_fp stamped on every member
devblock, fails outright with no partial claim.

blk_meta_relocate_devblock(): the real migration primitive -- bridges
the existing FORTH-block-granularity blk_subsys_relocate_block() up to
devblock granularity (BLK_PACK_RATIO=3, corrected mid-design), running
it 3x and transferring blk_meta_t ownership fields. The "migration
state machine" turned out to be just the 2 states BLK_FLAG_MIGRATING
already reserved; the real design work was the trigger. Two were
scoped in conversation (overflow onto Artemis; heat-based wear
leveling); heat/wear-leveling is built and wired into sk_repl_idle()
via blk_meta_t.write_count. Overflow is deliberately left open,
precisely scoped (needs a slot-lookup-by-device-pointer call site
threaded from WIREBIND) rather than guessed at.

Also flagged, not fixed: BMAPFMT's owner_fp/CLAIMED and the pre-existing
BAM allocator are two parallel, unreconciled accounting systems --
FIRSTTOUCH/relocate only touch the former.

Verified 3-arch boot to ok> (amd64/aarch64/riscv64, each in the
foreground); logs and DoE CSVs from this session's verification runs
included per this repo's own audit-artifact convention.

Co-Authored-By: Claude Sonnet 5 <noreply@anthropic.com>
Claude-Session: https://claude.ai/code/session_019YcT3H2PQeyujrzjqS3Var

src/starkernel/repl.c

@@ -325,6 +325,16 @@ static void sk_repl_idle(VM *active_vm)
      * did not survive a reboot until this fix. */
     blk_vm_flush_all(active_vm);
 
+    /* FABRIC-3.md §I.2, built 2026-09-04: heat/wear-leveling migration
+     * trigger -- one linear scan of Artemis's own device per idle tick
+     * (same ~1 Hz SK_IDLE_BEAT_INTERVAL cadence this whole function
+     * already runs at, chosen so a hot devblock is caught proactively
+     * rather than only on a failed write). See block_subsystem.c's own
+     * doc comment on blk_migration_idle_check() for what's built (heat-
+     * based relocation) vs. deliberately left open (overflow-triggered
+     * migration, needs a call site threaded from WIREBIND). */
+    blk_migration_idle_check();
+
     /* FABRIC-3.md Phase C (2026-08-28): distributed messaging pump. Every
      * live VM except Hera herself now owns its own MSG-ARENA/CH-ARENA and
      * MSG-TICK word (see capsules/common/messaging.4th) instead of only