Observability: integrate sc-observability 2.0 full OTel (Tokio) for task-activity visibility; tracks Phase D prerequisites

[randlee]

Tracking issue linking atm-core's next observability phase to the sc-observability work it depends on. Rand, 2026-09-26: full visibility on all task activity (every assignment, start, reminder, reset, escalation, close, prompt handoff) plus other daemon metrics, using the full OTel implementation (Tokio), not the lightweight Python-oriented one.

What atm-core has today (develop)

• Cargo.toml: sc-observability, sc-observability-log, sc-observability-types pinned =1.4.1. Logging only; no sc-observe, no sc-observability-otlp, no spans or metrics.
• crates/atm-observability/src/lib.rs: RetainedLogger adapter over Logger::builder_typed/try_log_typed/flush_typed.
• crates/atm-observability/src/tracing_bridge.rs: hand-rolled 700-line tracing-subscriber layer (TracingBridgeLayer), installed by crates/atm-daemon-bootstrap/src/daemon_observability.rs::install_tracing_bridge and registered by diagnostic_timeline.rs for its counters. Exists because 1.4.1 has no tracing/log bridge.
• Task activity is already typed but never reaches ObservabilityPort: TaskEventKind, TaskTransition, PromptHandoff in crates/atm-storage/src/task_state.rs; writers in atm-storage-rusqlite/src/task_store.rs, atm-http-runtime/src/herdr_queue_wake_escalation.rs, atm-http-runtime/src/prompt_handoff_record.rs.
• Related fixes in flight: task reminders: budget counts from task start while the assignee is between turns; lead_notified nudge sat unread #1598 (reminder reset, every-10 escalation, deferred escalation nudge, new reminders_reset ledger event), atm task history: the past N tasks of a team, including completed ones #1599 (atm task history).

sc-observability prerequisites (all in Phase D, ships as 2.0; plan on PR randlee/sc-observability#223, beads import randlee/sc-observability#221)

Need	sc-observability item	Status
Constructor accepting a host-owned Logger so info!/warn!/#[instrument] share the daemon's retained logger (replaces the hand-rolled bridge)	randlee/sc-observability#204 → sprint d-2 attach_logger(Arc<Logger>, AttachmentOptions)	open, planned
Typed sink registration without the deprecated LogSinkError	randlee/sc-observability#203 → sprint d-3 register_typed_sink	open, planned
Error enums 2.0 (breaks TryLogFailure/LogFailure/*_typed matches in atm-observability and crates/atm/src/main.rs)	randlee/sc-observability#92 → sprints d-4, d-12	open, planned
Neutral signal model (SpanKind, MetricValue::{Sum,Histogram}, ExporterBackend::OpenTelemetrySdk, TelemetryHealth)	sprint d-5, d-12	planned
Full OTel backend on Tokio: official opentelemetry SDK, gRPC/HTTP-protobuf, shutdown_async_typed	sprints d-6, d-7	planned
Public consumer surface, 2.0 release, migration guide	sprint d-18 (d-9 conformance after)	planned

Today's sc-observability-otlp 1.4.1 buffers all three signals into no-op exporters with crate-private exporter traits, so nothing can be exported before d-18. The legacy HTTP/JSON path (d-8) is the lightweight implementation and is not atm-core's target. Note: the legacy OTLP source Phase D restores came from atm-core (docs/plans/phase-d/legacy-otlp-provenance.json → randlee/agent-team-mail 7b39f4e7f).

atm-core work that does not wait for Phase D

1. Define the task-activity Observable payload and the ATM-owned mapping spec (sc-observability docs/atm-adapter-mapping-spec.md §4.2, §4.3, §9 leave span rules to ATM): which task events open/annotate/close a span, counters per TaskEventKind, latency histograms assign→start and start→close, prompt-handoff attempts.
2. Route the ledger writers above through ObservabilityPort so the events exist as observations before an exporter does.
3. Prepare the 1.4.1 → 2.0 adapter migration (error enums, attach_logger replacing TracingBridgeLayer while keeping the retained field allowlist and the diagnostic-timeline counters).

Process

Rand's sequence: import the sc-obs skill/agent system into atm-core in one PR, then write this phase's plan as beads with the atm-beads skill. This issue is the anchor the plan links to.

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