debug: standardize callTracer output and add debug_traceCall

[MysticRyuujin]

Specifies the callTracer output (undefined until now) for debug_traceTransaction,
debug_traceBlockByNumber/ByHash, and a new debug_traceCall. Same approach as the
opcode-tracer spec (#762); other named tracers keep the unconstrained escape-hatch branch.

Backed by a six-client hive rpc-compat run reproducible from this repo's fixtures. Per-client
conformance below.

What's in it

• CallFrame / CallLog / CallTracerConfig / CallTracerBlockEntry
  (src/schemas/call-tracer.yaml) — per-field presence/omission rules; recursion via an $id
  self-ref.
• debug_traceCall: GenericTransaction + optional block param (default latest) +
  TraceCallConfig (reuses the eth_simulateV1 overrides). A revert is not a JSON-RPC error.
• Tooling: specgen passes absolute-URI $refs so the recursive schema survives; speccheck now
  selects the anyOf branch by the requested tracer — without it, trace-result validation was
  vacuous (including the existing opcode branch). Negative tests included.
• Test chain: regenerated from upstream hivechain, which now carries the calltree contract and
  the tx-calltree / tx-callrevert modifiers (cmd/hivechain: add calltree contract and tx mods for callTracer testing hive#1587, merged), so the fixtures exercise nested
  call trees — inner reverts, STATICCALL write protection, DELEGATECALL logs, CALLCODE,
  precompile calls, and CREATE followed by SELFDESTRUCT. Every fixture is refilled because the
  block hashes change; the chain parameters are otherwise unchanged (-lastfork bpo2 -length 54).

Decisions already baked into the spec (raise it if you object, but these are settled by the
data, not open for a round-trip):

• error is exactly "execution reverted" for REVERT, free-form otherwise — the only string all
  clients agree on.
• root gasUsed = receipt gasUsed (4/5 clients; besu to align).
• reverted-frame logs are cleared (receipt consistency; reth to align).

Conformance — 32 debug_trace* fixtures replayed per client via hive rpc-compat, 2026-07-29:

Client	Version	Result	Changes needed
go-ethereum	v1.17.6-unstable	32/32 ✅	make debug_traceCall block param optional (one-liner, see below)
erigon	3.7.0-dev	32/32 ✅	none
nethermind	1.40.0-unstable	32/32 ✅	none
reth	2.4.1	26/32	error-path only: returns -32001 where the spec/reference returns -32000 on an out-of-range block in debug_traceCall, plus trace-genesis and two block-not-found cases
besu	26.7-develop	26/32	honor onlyTopCall (still returns nested calls); accept a block-hash param in debug_traceCall; two opcode-tracer storage-encoding cases
ethrex	v22.0.0-main	2/32	debug_trace* not usable yet; tracked as not-yet-implemented, not a conformance gap

Erigon and Nethermind are now fully green, and besu's gaps have narrowed considerably since the
earlier survey — withLog/logs, the chained-DELEGATECALL from, the CREATE to and the root
gasUsed all pass now.

One thing I need a nod on: debug_traceCall's block param is spec'd optional, default
latest (matching #812/#814). That needs a one-line geth change (follow-up PR). If we'd rather
keep it required, say so and I'll drop it.

One thing left open — logs[].index: spec'd optional and undefined for now. It's the only
field the geth family disagrees on — geth block-global (receipt index), erigon/reth tx-local
(each recomputing under onlyTopCall), nethermind omits it: three meanings plus an absence.
Can't be standardized without forcing two clients to change for a value nothing depends on, so
I'm flagging it rather than blessing one — fine to leave undefined unless someone needs it.
(position, its neighbour, is standardized.)

Glamsterdam follow-up: this specs the fork-independent frame shape only. The EIP-8037
two-dimensional gas fields (regularGasUsed/stateGasUsed/gasRefund) proposed in #852 are the
natural next layer — CallFrame leaves additionalProperties open, so they drop in as optional
fields once Glamsterdam is scheduled and clients emit them, without reopening this spec. Thanks
@qu0b for the EIP-8037 groundwork and the client survey.

Draft because: the cross-client divergence report is still to follow, and the
debug_traceCall block-param question above needs an answer. ethereum/hive#1587 is merged and
this branch is rebased on main with the chain regenerated from upstream hivechain, so the
fixtures are fully reproducible. ethereum/hive#1588 is still open; until it lands, hive enforces
the exact-match tracer fixtures but validates the speconly subset only vacuously. speccheck
enforces those fixtures at generation time, so that is a hive reporting gap, not a spec gap, and
no longer a hard blocker here.

The conformance run above is reproducible from this branch's fixtures with hive rpc-compat; the
exact invocation, and the client-file needed to pin each client, are noted in
GLAMSTERDAM.md.
That branch is a separate Glamsterdam integration superset — nothing in this PR depends on it, and
this spec is deliberately fork-independent.