feat(profiles): unified emission Phase 1 — target-aware driver_key, __adapters__, Profile.emit()

[discreteds]

What

Phase 1 (settings substrate) of the unified profile→kwargs emission design
(spec).
Generalizes the settings Profile so a single profile can emit different SDK
kwarg shapes per target (e.g. paramiko vs http vs boto). Additive and
fully output-back-compatible — bare-string driver_key specs are byte-for-byte
unchanged; target-scoped profiles fail closed.

This is the dependency-free foundation. Phases 2 (auth-client adapters +
TargetFamily + rule-4 invariant) and 3 (transport wiring + _core/auth
deletion) build on it and ship separately.

Changes

• ParameterSpec.driver_key: str | None → str | dict[Hashable, str] | None.
  A bare string maps for every target; a dict scopes per target. Excluded from
  the frozen-dataclass hash (field(hash=False)) so dict-scoped specs stay
  hashable (stays in __eq__).
• Profile._default_kwargs(target=None): now target-aware via the new
  _resolve_driver_key helper (None→None, str→all targets, dict→.get(target)).
• Adapter type alias (Callable[[Profile, dict], dict], 2-arg compose) +
  _UNSET sentinel, exported from mountainash_settings and
  mountainash_settings.profiles.
• Profile.__adapters__: per-target adapter map ({target: Adapter}). The
  legacy 1-arg __adapter__ (owns-pipeline) is retained, unchanged.
• Profile.emit(target=_UNSET, *, base=None): three-tier dispatch
  (driver_key renames → per-target __adapters__ 2-arg → legacy __adapter__
  1-arg → merged), fail-closed targeting, shallow-copy of caller-owned base.
• spec_invariants_for's test_driver_keys_unique: rewritten to per-target
  uniqueness (a dict driver_key is unhashable; the old set() would crash once
  a registry holds a scoped spec — which Phase 2's AUTH_REGISTRY will).

Notes

• Reconciliation: the spec's emit() pseudocode conflated the new 2-arg
  adapters with the legacy 1-arg __adapter__; this implements the corrected
  split dispatch (also patched back into the spec).
• Final-review fix: an explicit None target on a target-scoped profile was
  bypassing the unknown-target guard and silently emitting {}. Fixed to fail
  closed unless None is a registered target — matching the spec's emission
  safety contract. Covered by test_targeted_profile_explicit_none_target_raises.

Testing

• hatch run test:test — 441 passed (8 new test classes in
  tests/unit/profiles/test_emit.py; existing suite unchanged).
• hatch run ruff:check src tests — clean.

Implemented via subagent-driven development from
docs/superpowers/plans/2026-06-12-unified-emission-phase1-settings.md
(Codex-accepted plan); every task TDD'd and reviewed.

🤖 Generated with Claude Code

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