Decompose Step 6 snapshot: 140 task specs + contract docs

Closes out greenfield Step 6 (Decompose) for all 14 components
(C1-C13 + cross-cutting helpers/replay). Covers tasks AZ-266..AZ-446
plus the _dependencies_table.md and component contract documents.

State file updated to greenfield Step 7 (Implement), not_started.

Co-authored-by: Cursor <cursoragent@cursor.com>

_docs/02_tasks/todo/AZ-269_config_loader.md

@@ -0,0 +1,104 @@
+# Config Loader + Outer Config Container
+
+**Task**: AZ-269_config_loader
+**Name**: Config Loader
+**Description**: Implement `load_config(env, paths) -> Config` and the outer frozen `Config` dataclass. Merges env vars + one or more YAML files + documented defaults with strict precedence (env > YAML > defaults), returning an immutable container that holds one nested dataclass field per component slug.
+**Complexity**: 3 points
+**Dependencies**: AZ-263_initial_structure
+**Component**: shared.config (cross-cutting; epic AZ-246 / E-CC-CONF)
+**Tracker**: AZ-269
+**Epic**: AZ-246 (E-CC-CONF)
+
+## Problem
+
+ADR-001 (runtime selection by config) and ADR-009 (composition root) both require a single source of truth for configuration. Without a shared loader with explicit precedence rules, components silently fall back to defaults, the composition root grows local config-parsing logic, and operators cannot reliably override settings via env in CI or by YAML in the field.
+
+## Outcome
+
+- `load_config(env, paths)` is the only function any onboard process uses to materialise its `Config` at startup.
+- Precedence is deterministic and observable: env > YAML > defaults; later YAML files win over earlier ones; missing keys fall to defaults.
+- The returned `Config` is frozen end-to-end (every nested component block is also frozen) so accidental mutation by component code is a TypeError.
+
+## Scope
+
+### Included
+
+- `load_config(env: Mapping[str, str], paths: Sequence[Path]) -> Config` per the composition_root_protocol contract.
+- Outer frozen `Config` dataclass with one nested field per component slug. The OUTER container is owned by this task; the per-component nested dataclasses are owned by each component's epic and registered into the outer Config via a documented extension mechanism (a registry function called from `runtime_root.py`).
+- Documented default values for cross-cutting blocks only (logging level, FDR queue size, etc.). Per-component defaults live in their own component epics.
+- Friendly error messages when a required env var is missing (per AZ-263 AC-8): the error names the offending variable and points to `.env.example`.
+
+### Excluded
+
+- `compose_root` and `compose_operator` — owned by the next PBI in this epic.
+- Per-component config blocks — owned by each component epic.
+- The runtime self-check that strategies are linked — owned by the next PBI (StrategyNotLinkedError).
+
+## Acceptance Criteria
+
+**AC-1: Precedence env > YAML > defaults**
+Given env sets `LOG_LEVEL=DEBUG` and YAML sets `log.level=INFO`
+When `load_config(env, [yaml_path])` runs
+Then `config.log.level == "DEBUG"`
+
+**AC-2: YAML > defaults when env is silent**
+Given env has no `LOG_LEVEL` and YAML sets `log.level=INFO`
+When `load_config(env, [yaml_path])` runs
+Then `config.log.level == "INFO"`
+
+**AC-3: Defaults fill gaps**
+Given env has no `LOG_LEVEL` and YAML omits `log.level`
+When `load_config(env, [yaml_path])` runs
+Then `config.log.level` equals the documented default
+
+**AC-4: Multi-file YAML merge order**
+Given two YAML paths where the second sets `fdr.queue_size=8192` and the first sets it to `4096`
+When `load_config(env, [first, second])` runs
+Then `config.fdr.queue_size == 8192` (later file wins)
+
+**AC-5: Frozen end-to-end**
+Given a loaded `Config`
+When component code attempts `config.log.level = "DEBUG"`
+Then a `TypeError` (or `FrozenInstanceError`) is raised
+
+**AC-6: Required-var missing fails fast with pointer**
+Given a required env var is unset and no YAML override or default exists
+When `load_config(env, paths)` runs
+Then it raises an error whose message names the missing var and points to `.env.example`
+
+## Non-Functional Requirements
+
+**Performance**
+- Cold-start `load_config` ≤ 250 ms on Tier-2 (allocates the budget for the rest of compose_root within 1 s).
+
+**Reliability**
+- Loader is pure: same env + same file contents always yields a deep-equal `Config`. Verified by AC-relevant unit test.
+
+## Unit Tests
+
+| AC Ref | What to Test | Required Outcome |
+|--------|-------------|-----------------|
+| AC-1 | env vs. YAML for `log.level` | env value wins |
+| AC-2 | YAML vs. default | YAML value wins |
+| AC-3 | All-default for `log.level` | documented default returned |
+| AC-4 | Two YAML files, conflicting key | later file wins |
+| AC-5 | Mutation attempt on loaded Config | TypeError / FrozenInstanceError |
+| AC-6 | Missing required env var | error message names the var + points to `.env.example` |
+| NFR-perf | Microbenchmark `load_config` over a representative config | p99 ≤ 250 ms on Tier-2 |
+| NFR-reliability | Call `load_config` twice with same args | deep-equal `Config` instances |
+
+## Constraints
+
+- Public surface frozen by `_docs/02_document/contracts/shared_config/composition_root_protocol.md` v1.0.0.
+- No new dependency beyond what AZ-263 / E-BOOT pinned (stdlib + the YAML library already in `pyproject.toml`).
+
+## Risks & Mitigation
+
+**Risk 1: Per-component defaults drift across components**
+- *Risk*: Without a documented registration mechanism, two components may both claim a `log.level` default and conflict.
+- *Mitigation*: Defaults registry is keyed by component slug + key; collisions raise at registration time, not at load time.
+
+## Contract
+
+This task produces (jointly with AZ-NN compose_root) the contract at `_docs/02_document/contracts/shared_config/composition_root_protocol.md`.
+Consumers MUST read that file — not this task spec — to discover the interface.