Dogfood otel-scrape in devenv tasks

[schickling-assistant]

Problem
otel-scrape was implemented and validated as a wrapper, but effect-utils itself was not yet using it across its own build/dev quality gates. That left the dogfooding phase of #866 open and made task-level OTEL gaps easy to reintroduce.

Goal
Route effect-utils devenv task execution through otel-scrape by default while preserving script-visible behavior, local summary fallback, and the existing otel-span task spans.

Decisions

• Layer otel-scrape outside the existing trace.nix otel-span wrapper, preserving current devenv.task.* spans while adding wrapper-owned command/process evidence.
• Keep dogfooding transparent and reversible with OTEL_SCRAPE_DOGFOOD=0; missing otel-scrape falls back to the original task body.
• Write summary evidence to tmp/otel-scrape-dogfood/summaries by default so contributors get local proof without an OTLP backend.
• Add otel-scrape:dogfood-audit to check:* to fail when active task modules add unwrapped exec/status scripts.
• Keep future adapters behind the vertical-slice admission gate; candidate adapter names remain rejected until structured-source, privacy, degradation, registry, and consumer evidence exists.
• Keep ptrace-experimental opt-in; exact-by-default process observation remains helper-gated rather than ptrace- or snapshot-backed.

Verification

• nix build .#otel-scrape --no-link passed.
• OTEL_SCRAPE_SUMMARY_DIR=tmp/m19-dogfood-verify devenv tasks run genie:prepare --no-tui passed and produced otel-scrape.summary/v1 direct-child degraded process evidence.
• OTEL_SCRAPE_SUMMARY_DIR=tmp/m19-dogfood-verify devenv tasks run otel-scrape:dogfood-audit --no-tui passed.
• CARGO_TARGET_DIR=$PWD/tmp/m20-cargo-target RUSTC_WRAPPER= CI=1 devenv shell cargo test --manifest-path packages/@overeng/otel-scrape/Cargo.toml passed.
• CI=1 OTEL_SCRAPE_SUMMARY_DIR=tmp/m20-check-all-final devenv tasks run check:all --no-tui passed.

Friction & bottlenecks

• Dogfooding exposed an undeclared Nix check dependency: the node-cpuprofile package test required Node but the derivation did not declare it.
• The first full check:all run hit resource-contention timeouts in package tests; the affected lanes passed individually, and the final cached full gate passed after deterministic fixture updates.

Refs #866.