[FLO-OBS-05] Build the selected reusable observability package

[szmyty]

Parent: #14
Depends on: FLO-OBS-04 / #18

Outcome

If #18 selects a shared package, implement and publish the smallest independently usable Rust observability support layer proven by the pilots.

Until #18 is accepted, this issue remains a conditional execution checkpoint. If repository-local adapters are selected, close or reshape this issue with the decision evidence rather than creating a package anyway.

Scope

The selected package should own only cross-cutting mechanics and policy projections:

• composable tracing layers and an embedding-safe subscriber builder;
• fallible CLI initialization that never panics when a subscriber already exists;
• human stderr and JSON Lines stderr/file formatting presets;
• verbosity/filter/color/terminal/sink configuration resolved from explicit inputs;
• common resource/event/field helpers from [FLO-OBS-01] Define the suite observability, privacy, and stream contract #15;
• source-aware redaction and defense-in-depth field filtering;
• bounded asynchronous writer/flush guards;
• OpenTelemetry bridge configuration and resource mapping;
• optional OTLP exporter integration proven by [FLO-OBS-03] Prove opt-in OpenTelemetry logs, metrics, and traces #17;
• W3C context extraction/injection helpers with explicit allowlists;
• in-memory sinks/exporters and conformance-test helpers;
• a narrow diagnostic API for initialization/export failures.

The package must not own:

• product command parsers;
• domain diagnostics or error categories;
• run manifests, evidence, checkpoints, artifacts, or validation;
• provider selection or execution;
• global subscriber policy for embedding applications;
• product-specific event vocabularies beyond registered common fields;
• CLI banner artwork.

Feature and dependency design

Use evidence from #18 to finalize names, but preserve these properties:

• Minimal default feature set with no network exporter.
• Human formatting, JSON Lines, file rotation, OpenTelemetry bridge, OTLP transport, and test support are independently selectable where practical.
• Unsupported or unsafe feature combinations fail at build/configuration time.
• OpenTelemetry dependencies and runtime/TLS choices remain optional.
• No async runtime becomes mandatory for consumers that use only local human logging.
• Supported MSRV and edition are explicit.
• unsafe is forbidden unless an accepted decision explicitly authorizes a narrowly audited use.
• Dependency licenses, advisories, provenance, SBOM, and update ownership are recorded.
• Public APIs use semantic versioning and expose builders/layers rather than product-specific macros wherever possible.

Required behavior

• Constructing a layer does not install it globally.
• CLI convenience initialization returns a typed result and a lifetime/flush guard.
• Repeated or embedding-controlled initialization never panics.
• Dropping/shutting down the guard has a bounded duration.
• Export and file sinks remain inactive unless explicitly configured.
• Sensitive wrapper types cannot be accidentally formatted into ordinary fields without an explicit reveal operation.
• Metric labels pass cardinality/privacy validation.
• Trace propagation helpers refuse unapproved destinations.
• Telemetry failures never mutate a domain outcome implicitly.
• Human formatting remains accessible without color.

Acceptance criteria

• The package location, name, owners, release process, MSRV, and feature matrix match accepted [FLO-OBS-04] Decide shared observability crate and repository ownership #18 evidence.
• Default builds perform no network access and avoid exporter/network dependencies.
• Layer-only embedding and CLI convenience initialization are both demonstrated.
• Human, JSON Lines, rotating-file if selected, in-memory, and OpenTelemetry modes have focused tests.
• Redaction covers secrets, environment values, argv, URLs/headers, paths, source-derived content, and error chains.
• Queue, truncation, rotation, flush, timeout, shutdown, and exporter failure are bounded and tested.
• Feature-disabled and feature-enabled MSRV/platform matrices pass.
• Package contents, licenses, SBOM/provenance, docs, examples, changelog, and compatibility policy are release-ready.
• An immutable pre-1.0 release is published and consumable without a source/path dependency.
• A rollback guide explains how a holon returns to its repository-local adapter.
• No holon must release in lockstep with the package.

Explicit non-goals

• Migrating every product; [FLO-OBS-06] Migrate the suite and enforce observability conformance #20 owns adoption.
• Hosted infrastructure.
• Export enabled by default.
• Domain event/evidence schemas.
• CLI branding.
• Continuous profiling.
• Direct dependencies among sibling holons.

Roadmap-Track: FLO-OBS