Workcell handoff: implement host-neutral Codectx compositor vertical slice

[greygoody]

Implementation workcell handoff

Status

workcell_id: codectx-compositor-v0
state: ready
base_repository: greygoody/codectx
base_branch: main
base_commit: 9593648f09540b8522885d8ff1a014970d28488e
scope: implementation

Mission

Implement the smallest deterministic, host-neutral compositor slice that adapts the current repository lens, accepts one synthetic managed lens, applies one explicit move, and emits one surface-independent projection.

Canonical steering input:

• docs/steering-v0/architecture.md
• docs/steering-v0/migration-plan.md
• docs/steering-v0/downstream-workcells.md

Accepted steering evidence:

• greygoody/orb-eval#16
• data/contributions/v1/codectx-steering-2026-06-30/steering-workcell/codectx-ambient-hud-v0/

Required scope

• versioned experimental contracts for lens contribution, attention item, projection, and move;
• fail-closed validation for unsupported versions;
• adapter from ContextPacket v1 into a repository-lens contribution;
• one synthetic managed-runtime lens fixture;
• deterministic compositor policy sufficient for the accepted scenarios;
• one in-process reference host;
• machine-readable projection trace;
• compatibility tests for current CLI and JSON output.

Required scenarios

1. healthy repository and runtime state collapses;
2. unexpected repository change creates attention;
3. managed urgent warning becomes visible;
4. contradictory repository and managed contributions remain separately attributed;
5. acknowledgement changes attention state, not source truth;
6. compositor recreation recomputes derived state;
7. unsupported contribution version fails closed;
8. missing mandatory lens produces degraded state.

Non-goals

• Orb or Codex integration;
• Codectx App package;
• daemon, database, network, or marketplace;
• durable persistence beyond fixtures;
• semantic retrieval;
• generalized policy language;
• new visual UI;
• changing current v1 surfaces.

Required proof

• formatting, linting, unit tests, and integration tests;
• current just check witnesses remain green;
• repeated deterministic fixture run;
• exact projection trace;
• changed-path and dependency-boundary report;
• contribution-only evidence recorded in greygoody/orb-eval.

Stop conditions

Stop and report when implementation requires a host-specific dependency, changes ContextPacket v1, invents source authority, resolves domain contradiction, or regresses current CLI compatibility.

Completion

The workcell closes when one coherent in-process slice passes all scenarios and produces a reviewable contract for host integration.