Crate turul_a2a_patterns 

turul-a2a-patterns defines reusable abstractions for A2A skill authoring — the SkillHandler trait, SkillRegistry, SkillCard (SKILL.md) helpers, and the SkillProgressSink trait. It depends only on turul-a2a-proto and turul-a2a-types, never on the server runtime. It does NOT change the A2A wire contract; profile/extension machinery lives elsewhere.

Public surface (all re-exported from the crate root):

• Errors: SkillError, SinkError, ManifestError, RenderError, ValidationError.
• Skill handler trait: SkillHandler taking a SkillProgressSink for non-terminal status / artifact emits.
• Progress sink: SkillProgressSink + ProgressState (non-terminal states only; terminals come from the handler’s return value).
• Pre-terminal gates: PreTerminalGate + GateContext, run on a handler’s output by GatedHandler; a gate error replaces it.
• Terminal hook: TerminalHook + SkillOutcome.
• SKILL.md projection: SkillCard (from_embedded, from_skill, TryFrom<&Skill>, validate_input, validate_output, render_prompt, to_agent_skill) + ExecutionHints. turul-agent-skills loads and validates the SKILL.md; this crate reads its a2a-* metadata and asset files.
• Registry: SkillRegistry trait + InMemorySkillRegistry + SkillDescriptor.
• Schema validation: validate_json (JSON Schema 2020-12 strict-keyword check).

Internal modules (error, sink, handler, gate, hook, manifest, template, schema, registry) are implementation detail; use the flat re-exports above.

Structs

ExecutionHints

Provider-neutral execution hints.

GateContext

What a gate sees: the skill id, the invocation params and the output the handler produced.

GatedHandler

A SkillHandler that runs its gates on the inner handler’s output.

InMemorySkillRegistry

Default in-memory SkillRegistry.

SkillCard

The A2A view of an Agent Skills SKILL.md.

SkillDescriptor

Returned by SkillRegistry::describe.

Enums

ManifestError

Structured manifest parse error.

ProgressState

Non-terminal task states a skill may emit during execution. Terminal states are framework-owned; not constructible here.

RenderError

Structured template render error.

SinkError

Sink-side error variants.

SkillError

Skill error surface. Exactly three variants; richer error shapes are the adopter’s concern at the call site.

SkillOutcome

Outcome of a skill execution observed by a terminal hook.

ValidationError

Structured I/O schema validation error.

Traits

PreTerminalGate

A check that can veto a successful skill output.

SkillHandler

A handler that runs when a skill is invoked.

SkillProgressSink

Object-safe progress emission trait used by SkillHandler::run.

SkillRegistry

Registry mapping AgentSkill.id to a registered SkillHandler.

TerminalHook

Post-execution hook fired after SkillHandler::run returns.

Functions

validate_json

Validate instance against schema (JSON Schema 2020-12).