feat: Add ACP, Spaces, and Agent Registry for Devin Desktop integration

[Keramikus-97]

Summary

Implements three modules enabling this integration to work with Devin Desktop and the Agent Client Protocol (ACP) ecosystem. Agents like OpenCode, Codex, and Claude can now register, share context via Spaces, and be managed through a Kanban-style command center.

New modules:

acp.py — Agent Client Protocol

msg = ACPMessage.create(ACPMessageType.REGISTER, sender_id="agent-1", recipient_id="editor-1")
reg = build_opencode_registration()  # pre-configured with code_review, slash_commands, etc.
version = negotiate_version(["1.0", "1.1"])  # highest mutual version (numeric comparison)
validated = validate_message(raw_dict)  # strict type checking on all fields

spaces.py — Shared Context Containers

space = create_space("PR Review", owner_id="opencode-1")
space.add_context(create_context_item(ContextItemType.PR, "PR #5", "Fix bug", "opencode-1"))
results = space.search_context("bug")
merge_spaces(target, source)  # combine contexts, members, and tags (deduped)

agent_registry.py — Multi-Agent Lifecycle Management

registry = AgentRegistry(heartbeat_timeout=60.0)
registry.register(build_opencode_registration(agent_id="oc-1"))
registry.assign_task("oc-1", "Review PR #10")  # rejects ERROR/OFFLINE/SHUTTING_DOWN agents
reviewers = registry.find_by_capability("code_review")
board = registry.to_kanban()  # {"idle": [...], "busy": [...], "error": [...]}

Review fixes (commit 2 — round 1)

• __init__.py now exports all public functions, not just data types
• Removed redundant timestamp from heartbeat payload
• remove_from_space returns False when space_id wasn't in agent's list
• LearnerProfile.add_xp uses running total instead of O(n²) re-summing
• validate_message rejects non-string correlation_id values

Review fixes (commit 3 — round 2)

• RegisteredAgent.to_dict() now includes capability parameters (was silently dropped — ACPRegistration.to_dict() included them but RegisteredAgent.to_dict() didn't)
• negotiate_version uses numeric version comparison instead of lexicographic sort ("9.0" no longer sorts above "10.0")
• validate_message rejects non-string message_id, sender_id, recipient_id, protocol_version (previously str(None) → "None" was silently accepted)
• LearnerProfile.xp_progress uses O(1) closed-form 100 * level * (level-1) // 2 instead of O(n) sum()
• merge_spaces now merges tags from source into target (was only copying items and members)
• assign_task rejects agents in ERROR/OFFLINE/SHUTTING_DOWN states (previously overwrote status to BUSY)

232 tests, 99% coverage.

Link to Devin session: https://app.devin.ai/sessions/e783b2864bf3411f8832faec6c5f93bf
Requested by: @Keramikus-97

[Keramikus-97]

[devin-ai-integration]

✅ Devin Review: No Issues Found

Devin Review analyzed this PR and found no bugs or issues to report.