v0.20.0 — retro follow-up: WildLake + ToughAnt + SwiftLynx + #11

Retro follow-up batch: fixes the three lightest action items from the
v0.19.2 retrospective (WildLake, ToughAnt, SwiftLynx). The two heavier
retro items — SharpBrook (MCP schema hot-reload) and SnappyBird
(data-repair path for append-only LogEntries) — are deferred to
v0.21.0 pending the design discussions opened as DISC-DaringBird and
DISC-WiseLily. See DEC-20260424_0101-SolidBadger-split-v0-20-0.

Added

• docs(AGENTS.md): "Sub-agent delegation" section. Pairs with the
  existing "Skill guards" list and codifies the read-only / mutating
  split for harness Agent-tool sub-agents: delegate Read, search
  Bash, and MCP query_* / get_* / search_* / list_*; keep
  Write, Edit, new mkdir, MCP create_* / transition_* /
  record_* / link_* / open_* / log_event, and git mutations
  on the main session. Closes
  BACK-20260424_0038-ToughAnt-ephemeral-sub-agent-defaults.

Changed

• feat(skill-gate): compliance-ack TTL is now an idle timeout.
  _any_valid_marker() in check_route_task_called.py now rewrites
  the matching marker's acknowledged_at to now on every
  successful gate check. A session that is actively making
  compliant writes no longer expires mid-flow (the v0.19.2
  midnight-span pain pattern); a session that goes idle for longer
  than _ACK_LIFETIME_HOURS (12h) still must re-acknowledge. Touch
  failures are non-fatal. Closes
  BACK-20260424_0038-SwiftLynx-compliance-contract-acknowledgement-ttl.

Fixed

• fix(skill-gate): remediation text uses the on-disk contract
  version. _remediation_msg() parses the leading
  <!-- pk-compliance vN --> marker in
  assets/compliance-contract.md rather than hard-coding v1. The
  v0.19.2 hard-code told callers to acknowledge v1 even though the
  on-disk contract was already v2. Part of SwiftLynx.
• fix(retrospective): /pk-retro --auto-workitems no longer fails
  with ModuleNotFoundError: No module named 'mcp'. pk_retro.py
  declared only pyyaml in its PEP 723 header, but its in-process
  MCP loader imports server.py modules from artifact-management,
  event-log, and workitem-management — all of which require
  mcp[cli] and jsonschema. Added both to the PEP 723 header so
  uv run --script pk_retro.py resolves them automatically. Closes
  BACK-20260424_0038-WildLake-pk-retro-auto-workitems.
• fix(skills): resolve cross-category retrospective skill
  basename collision. product/retrospective is renamed to
  product/sprint-retrospective (directory, name:, and id: SKILL-sprint-retrospective); the processkit-category
  retrospective (release scope, /pk-retro) keeps the bare name.
  Closes #11. The missing pk-doctor/commands/ directory
  (#10) and the duplicate pk-resume.md command
  (#12) were already resolved in v0.19.2 (90c980f and 87e185e
  respectively) and are closed here for bookkeeping.

Deferred to v0.21.0

• BACK-20260424_0037-SharpBrook-mcp-servers-cache-schemas — MCP
  schema hot-reload / reload_schemas tool. Design discussion:
  DISC-20260424_0101-DaringBird-how-should-mcp-servers.
• BACK-20260424_0038-SnappyBird-data-repair-path-for — data-repair
  path for malformed append-only LogEntries. Design discussion:
  DISC-20260424_0101-WiseLily-how-do-we-allow.

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