[KM-626] docs: record slow-path agent layer in PROGRESS

PROGRESS.md: 2026-06-08 entry for the slow-path agent (TaskRunner + Assembler +
Coordinator under agents/slow_path/), the Orchestrator-vs-slow_path naming, and
the open follow-ups (live wiring, real invoker swap, GPT-mini deployment).

Co-Authored-By: Claude Opus 4.8 <noreply@anthropic.com>

PROGRESS.md

@@ -2,11 +2,47 @@
 
 Persistent tracker mirroring the 42-item ownership table in `REPO_CONTEXT.md` "Team — division of work". Update as PRs land. Future Claude Code sessions read this to know what's already done.
 
-**Last updated**: 2026-06-08 (tool taxonomy + ownership revision — see "What just shipped" below)
+**Last updated**: 2026-06-08 (slow-path agent layer — TaskRunner + Assembler + Coordinator)
 **Current open PR**: `pr/1` — active. Cleanup PR committed and pushed.
 
 ---
 
+## What just shipped (2026-06-08 — KM-626: slow-path agent layer)
+
+The rest of the slow path after the Planner (KM-567), from
+`AGENT_ARCHITECTURE_CONTEXT_new.md` §7.4 / §7.5 / §8.2–8.4. Built and tested against
+mocks; **not yet wired into the live `ChatHandler`** (waits on the tool team's real
+`ToolInvoker` + a real `BusinessContext`). Fast path untouched.
+
+**Naming:** "Orchestrator" = the entry dispatcher only (`agents/orchestration.py`).
+The slow-path **workers** live in **`agents/slow_path/`** — deliberately NOT named
+"orchestrator".
+
+**Files added** (`src/agents/slow_path/`):
+- `schemas.py` — `TaskResult`, `RunState` (§8.2); `TaskSummary`, `AnalysisRecord`,
+  `AssembledOutput`, `AssemblerNarrative` (§8.3). Reuses `ToolOutput`.
+- `invoker.py` — `ToolInvoker` Protocol only (§8.4); the tool team owns the impl (KM-418).
+- `errors.py` — `SlowPathError`, `AssemblerError`.
+- `task_runner.py` — deterministic, 0 LLM: wave-based execution, `${t<id>}` placeholder
+  resolution, internal `validate_args`, never-throw invoke, status labeling,
+  degrade-and-continue → `RunState`.
+- `assembler.py` + `prompt.py` + `config/prompts/assembler.md` — single LLM call →
+  `AssemblerNarrative`; code merges with `RunState` to build the `AnalysisRecord`
+  (structured fields copied, never re-authored).
+- `coordinator.py` — `SlowPathCoordinator`: Planner → TaskRunner → Assembler.
+
+**Tests added** (`tests/agents/slow_path/`, 12 passing; gitignored): schema round-trips
++ chat_answer-first; runner happy/placeholder/parallel/degrade/arg-miss; assembler
+narrative-vs-snapshot + question threading; coordinator end-to-end. `ruff` clean;
+tool-agnostic (no `src/tools/*` import).
+
+**Open follow-ups (not blockers):** wire `SlowPathCoordinator` into the expanded
+Orchestrator/`ChatHandler` once the real invoker + `BusinessContext` exist; swap the
+test `MockToolInvoker` for the tool team's real one (zero agent change, INV-7); 4o →
+GPT-mini deployment swap.
+
+---
+
 ## What just shipped (2026-06-08 — tool taxonomy + ownership revision)
 
 Team decisions after the teammate pushed KM-624 (`src/tools/analytics/`):