ADR-008: Service Package and Transcript Boundaries

Context

The repository root is the public Go package:

github.com/easel/fizeau

That package is currently carrying more than the public contract. It contains the exported service API, concrete service execution, routing/status support, provider quota state, transcript/progress rendering, session-log mechanics, test seams, and a large test surface. This makes the package hard to reason about and makes downstream consumers more likely to treat implementation details as public behavior.

The same boundary problem exists at runtime. Fizeau owns native providers and subprocess harness adapters, but downstream consumers such as DDx have grown compensating code that parses harness-native streams, tails Fizeau session-log files, renders human progress lines, and infers runtime status from internal telemetry. That duplicates Fizeau concerns and creates drift between harnesses.

Pure no-op compactions are already silent in the agent loop: when the compactor returns the no-op signal, Fizeau emits no compaction start/end event. Any downstream policy that watches for repeated no-op compaction telemetry is therefore observing a stale or invalid signal.

Decision

1. Root package is the public facade

The root package fizeau is the compatibility boundary for external consumers. It should contain exported service interfaces, request/response types, event types, constructors, errors, compatibility aliases when needed, and public contract tests.

Concrete service implementation code should move behind internal packages. The likely end state is:

internal/serviceimpl
internal/transcript
internal/routehealth
internal/quota

This follows the official Go module layout guidance: an importable library package can live at the module root, commands live under cmd/, and private implementation packages live under internal/. This is a package-boundary change, not a module split. The module import path stays stable as github.com/easel/fizeau.

Do not create a nested fizeau/ package under this module. With the existing module path, that would either create the stutter import path github.com/easel/fizeau/fizeau or force the repository into a nested-module/workspace shape. Neither tradeoff is justified by this decision. Introducing additional go.mod modules is deferred until the internal boundaries have proven stable and a real multi-module need exists.

2. Public service types stay public

Public contract types should remain in the root package unless there is a separate, deliberate decision to create a public subpackage. Root aliases to an internal package are avoided because they make API identity and documentation harder to understand and can leak unimportable implementation paths into tooling.

Internal packages may depend on root public types only through narrow seams that avoid import cycles. If an implementation move exposes a cycle, the fix is to introduce smaller implementation-local interfaces or adapter functions, not to make the root package absorb implementation code again.

3. Fizeau owns transcript and progress semantics

Fizeau is the owner of:

• harness-native stream parsing;
• native-provider event normalization;
• public service event construction;
• tool call/result pairing;
• payload-size accounting;
• compact progress/status line rendering;
• session-log lifecycle and replay projections.

The canonical human-readable live line is the Fizeau-owned progress payload, currently ServiceProgressData.Message. It must remain bounded and suitable for downstream display without downstream parsing of prompts, tool input, tool output, or harness-native JSON.

Harnesses may differ internally, but once an interaction crosses the FizeauService boundary, downstream consumers should see the same public event vocabulary and required fields.

4. Downstream consumers are pass-through clients

DDx and other consumers may:

• call public FizeauService methods;
• forward or store public ServiceEvent values;
• display Fizeau-provided progress text;
• link or copy Fizeau-owned session artifacts;
• decode final/routing fields needed for their own bookkeeping.

They must not:

• parse harness-native streams such as Claude stream-json;
• synthesize Fizeau internal session events;
• tail and render Fizeau session-log JSONL as policy input;
• reconstruct tool transcripts for routing/retry decisions;
• infer runtime failure from private or historical Fizeau telemetry.

DDx still owns its own bead/worker lifecycle events: bead claimed, attempt started, review running, landed, preserved, failed, and similar outer workflow state. Those events are separate from Fizeau’s agent transcript.

5. No-op compaction is silent

Pure no-op compaction probes are not progress and are not telemetry for downstream policy. They remain silent at the public service boundary. Real compaction work and real compaction failures remain Fizeau runtime concerns.

Any stale API or downstream code that models a no-op compaction stall breaker must be removed in follow-on implementation beads.

Consequences

• The root package becomes smaller and easier to audit for public API compatibility.
• Implementation tests move with the packages that own the behavior.
• Transcript rendering becomes consistent across native, Claude, Codex, Gemini, Pi, and Opencode paths.
• DDx changes are blocked until Fizeau ships the public surface needed for pass-through consumption.
• Some refactors will be mechanically large; each implementation bead must keep source compatibility and run go test ./....

Implementation Implications

1. Delete stale no-op compaction stall policy from Fizeau.
2. Move concrete service implementation behind internal/serviceimpl.
3. Introduce internal/transcript for public event/progress construction.
4. Migrate native and subprocess harness event paths onto the transcript package.
5. Add conformance tests across supported execution paths.
6. Move route status, route attempts, burn-rate, and quota health code out of the root package.
7. Audit the root package and keep only public facade code plus public API smoke tests.
8. Tag a Fizeau release before downstream DDx changes consume the new surface.

Non-Goals

• No split into multiple Go modules in this decision.
• No public import path change.
• No change to routing policy or provider scoring.
• No removal of real compaction failure handling.
• No DDx implementation changes in this repository.