feat(core): Phase G — hierarchical subgraphs, role catalog, TaskNodeKind

[mmogr]

Summary

Implements Phase G of the v2 orchestrator architecture (closes #508): hierarchical task decomposition via TaskNodeKind::Team { subgraph }, a built-in role catalog, and team lifecycle SSE events.

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Changes

gglib-core — domain types

role_catalog.rs (new)

• RoleId newtype (pub struct RoleId(pub String)) with new(), as_str(), Display, Serialize/Deserialize
• RoleSpec — display name, system prompt fragment, default tool allowlist, suggested temperature, requires_approval flag
• RoleCatalog — HashMap<RoleId, RoleSpec> with Default impl populating 7 built-in specialist roles: researcher, red-team, fact-checker, writer, editor, critic, synthesizer

task_graph.rs

• New TaskNodeKind enum: Leaf (default) | Team { subgraph: Box<TaskGraph> } — serde snake_case, #[serde(default)] on the field for backward compat
• MAX_NODES / MAX_DEPTH docs clarified as per-subgraph limits
• MAX_TOTAL_NODES = 32 soft aggregate budget (not enforced yet — Phase H)
• TaskNode.role: Option<RoleId> — specialist role assignment
• validate_acyclic() recurses into Team subgraphs
• TaskGraph::total_node_count() — recursive aggregate count

events.rs

• TeamStarted { team_id, role: Option<RoleId> } — emitted before team subgraph begins
• TeamSynthesized { team_id, compacted_output } — emitted when team subgraph completes

mod.rs

• pub mod role_catalog added
• Re-exports: RoleCatalog, RoleId, RoleSpec, TaskNodeKind, MAX_TOTAL_NODES

Caller updates

• gglib-agent/orchestrator/director.rs — TaskNode construction gains kind: TaskNodeKind::Leaf, role: None
• gglib-agent/orchestrator/executor.rs — make_node() test helper updated
• gglib-proxy/src/orchestrator_proxy.rs — new event variants added to exhaustive match
• gglib-cli/src/handlers/orchestrate.rs — render_event() handles TeamStarted/TeamSynthesized
• gglib-proxy/tests/integration_virtual_models.rs — test_graph() helper updated

Test fixtures

• tests/fixtures/orchestrator/phase_f_baseline.json — Phase F regression fixture (flat graph without kind/role fields; verifies backward-compat deserialization)

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Tests

• 25 unit tests pass (cargo test -p gglib-core)
• All doc-tests pass (cargo test --doc -p gglib-core)
• cargo clippy --all-targets -- -D warnings — clean
• ./scripts/check_boundaries.sh — all PASS

Issue

Closes #508