docs: define modular local agent contracts

docs/development/MODULARITY_PROTOCOL.md

@@ -4,7 +4,7 @@
 
 ## Default structure
 
-Use a modular monolith for the service and a separate local-agent application. A module is a coherent responsibility with a public contract, private implementation and declared dependencies. It does not need its own process, repository or package release. Split deployment only when isolation, scaling or independent release needs justify it.
+Use a modular monolith for the service and a separate local-agent instruction pack executed by an existing host. A module is a coherent responsibility with a public contract, private implementation and declared dependencies. It does not need its own process, repository or package release. Split deployment only when isolation, scaling or independent release needs justify it.
 
 Every feature belongs to a named module. Consumers use its public interface; they cannot import private helpers, inspect its tables, edit its files or rely on provider-specific response objects. Cross-module payloads use GEWU-owned types. The composition root selects implementations and manages their lifetimes. Domain/application code cannot select a concrete implementation through scattered conditionals.
 
@@ -29,8 +29,8 @@ Compatibility is behavioral: valid inputs, errors, cancellation, ordering, idemp
 | Search and ranking | Scoped candidates, scores/explanations, revision and budget rules | Replace FTS/vector engine or ranking algorithm without modifying readers. |
 | Identity and credentials | Authenticated principal, capabilities, grants and revocation | Replace login backend without changing proposal authorization semantics. |
 | MCP and HTTP adapters | Versioned wire schemas and domain-error mapping | Update transport SDK without moving rules into routes. |
-| Agent model provider | Typed requests/results, usage, timeouts and declared capabilities | Change local/hosted provider without exposing SDK types to skills. |
-| Agent pipeline runner | Stage dispatch, bounded scheduling, checkpoints and outcomes | Replace orchestration library while preserving stage contracts and resume semantics. |
+| Agent host/model adapter | Profile discovery, model capabilities, tool access and execution metadata | Change configured host/model without baking provider syntax into shared skills. The host owns its provider SDK. |
+| Agent pipeline coordinator | Stage inputs/outputs, work budget, checkpoints and outcomes | Replace coordinating instructions while preserving skill contracts and resume obligations. The initial coordinator is host-executed Markdown, not a standalone engine. |
 | Skills and stage handlers | Declared inputs/outputs, tools, prompt/content versions and budget | Replace an extraction or assessment skill without rewriting the pipeline. |
 | Harness adapter | Profile/skill discovery and authenticated public tool access | Change a host's configuration format without duplicating the skill pack. |
 | Frontend feature modules | Route/data contract, component props, events and accessibility behavior | Replace an evidence viewer or result list while preserving API and navigation. |
@@ -40,7 +40,7 @@ Compatibility is behavioral: valid inputs, errors, cancellation, ordering, idemp
 
 Public contracts, implementation versions, persisted schemas and model/prompt artifacts have distinct identifiers. Use [semantic versioning](https://semver.org/) for declared stable contracts: compatible additions are minor, fixes are patch, breaking behavior is major. Before 1.0, explicitly list supported contract versions; do not assume every `0.x` update is compatible. Published immutable artifacts are never changed in place.
 
-Backend boundaries use typed ports with injected dependencies; the frontend imports feature public exports and shared primitives. Shared contract packages stay small and have no dependency on providers, storage engines or UI frameworks. Reject import cycles and cross-feature private imports in CI. The local agent cannot import service storage/auth internals; its GEWU access is through the public MCP client contract.
+Backend boundaries use typed ports with injected dependencies; the frontend imports feature public exports and shared primitives. Shared contract packages stay small and have no dependency on providers, storage engines or UI frameworks. Reject import cycles and cross-feature private imports in CI. Local-agent helper/connector code cannot import service storage/auth internals; its GEWU access is through the public MCP client contract.
 
 Configuration selects from installed, reviewed implementations by ID. Validate configuration and capability compatibility before activation. Do not discover executable modules from uploaded sources, skill text, arbitrary import strings or URL-supplied code. Python package entry points are a possible future distribution mechanism, not permission to auto-load third-party code; [the packaging guide](https://packaging.python.org/en/latest/guides/creating-and-discovering-plugins/) describes discovery mechanisms, not trust enforcement.