Show keccak-derived slots as derivations under their reserved row

[halaprix]

Implements docs/design/derived-slots-v1.4.md. Closes slotscope-xu8 (.1, .2).

What you see

slotscope-zvd gave every reserved slot a row but could not show what actually
lives in a mapping — those entries sit near 2^256, nowhere near the declared
sequence. They now appear as child rows under the head they descend from.

The address is the derivation, not the number. The rail reads
keccak(0xaa…, 1), or keccak(0xbb…, keccak(0xaa…, 2)) for a nested hop, or
keccak(3)+2 for an array element. That is the slot rail — the address column
everywhere else in this instrument (line numbers, PCs, slot numbers) — so a
derived entry's address is written the way the EVM computes it. The raw 32-byte
slot is a hover detail.

Entries that were only read are included and marked read-only. Nothing in the
product surfaced those before, and "read but never written" is worth teaching.

How a child finds its parent

From Layer-1 facts alone, never by parsing a display label. KeccakObservation
carries the exact preimage, so:

• a 64-byte input splits into key ‖ baseSlot — both halves exact;
• a 32-byte input is an array or data head, and elements sit at keccak(base) + delta;
• a nested hop hashes key ‖ innerHash, so the tail is followed until it is a
  declared slot.

Parent linkage is therefore slot arithmetic, not name matching. A head nested
inside a struct attaches with no special case, and the derivedCountByBase
name-matching gap noted in the v1.2 plan disappears rather than being patched.

buildRows stays compiler-only — the gapless invariant is about declared slots,
and a derived slot is not one — so children attach at the view layer.

Decisions worth keeping

• The child set spans the whole run, not stepIndex <= cursor. Roving focus is
  index-based, so a row appearing mid-scrub would move focus under the reader. The
  cursor changes values, never row positions.
• Orphans are visible. A touched slot whose derivation cannot be reconstructed
  gets its own honest heading instead of being dropped.
• RuntimeStorage becomes a write log in observation order with step numbers,
  keeping the status pill, migration badge and constructor-origin heading. The grid
  is the map; two maps of the same state, ordered differently, only made a reader
  decide which to believe. Its runtime-group e2e assertion is replaced
  deliberately.
• Roving focus now indexes a flat list of navigable rows, so arrow keys reach a
  child exactly like a declared slot.

Verification

Gate	Result
format:check, lint, typecheck	clean
test:unit	241/241 — new derivedRows suite runs real compiled contracts through the EVM, not hand-built layouts
test:e2e	62/62, including axe on a grid with derived children
fixtures:verify	no drift
release:verify	passed
build:check	225 KB main entry
benchmark:v0.1	p95 250 ms action-to-paint, 732 ms cold start — PASS

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Project	Deployment	Actions	Updated (UTC)
slotscope	Ready	Preview	Jul 30, 2026 3:02pm