fix: derive context_compaction capability from controls, remove has_hook config

[RjyavardhanSingh]

Problem

Fixes #138

context_compaction was the only policy with a has_hook flag — a host capability masquerading as governance config. Three defaults disagreed (code: True, yaml: false, Admin UI: false), and the shipped default was wrong for the documented integration path: wrap_complete already supplies the prompt-assembly hook, so every Tier-1 quickstart user has the hook but the config said they didn't.

The policy appeared enabled in the dashboard while silently doing nothing.

What changed

• Removed has_hook from ContextCompactionPolicy, build(), config template, default.yaml, Admin UI placeholder, and all example/benchmark configs
• Added compaction_supported to ApplyControls — set by wrap_complete which IS the hook
• Derived capability at runtime via a context variable (_current_controls) set in Governor._enforce(), so the policy reads controls instead of a config flag
• Logged a one-time warning when compaction degrades to telemetry (no hook available)
• Updated tests to exercise both paths (compaction supported / not supported)

Why this approach

Option 1 from the issue: "derive it." Capability belongs with actuator plumbing, not a governance record. wrap_complete advertises the capability because it IS the hook — correct by construction, no config needed.

A context variable avoids changing the Policy.decide() ABC (which would require updating all 10 policies).

Files changed

File	Change
src/tokenops/control/policies/context_compaction.py	Remove has_hook, derive from controls, add warning
src/tokenops/control/engine.py	Add compaction_supported to ApplyControls, set context var in _enforce()
src/tokenops/control/context.py	Add _current_controls ContextVar + helpers
src/tokenops/control/integration.py	Set controls.compaction_supported = True in wrap_complete
src/tokenops/control/config.py	Remove has_hook from template
src/tokenops/config/default.yaml	Remove has_hook
src/tokenops/ui/views/admin.py	Remove has_hook from placeholder
tests/test_context_compaction.py	Update tests for new API
tests/test_actuators.py	Remove has_hook from build call
tests/test_policies_wrap_integration.py	Remove has_hook from build call
benchmarking/*/configs.py (3 files)	Remove has_hook from configs
examples/config/*.yaml (5 files)	Remove has_hook from configs
docs/policies/context_compaction.md	Document where hook comes from
CHANGELOG.md	Document behaviour change

Acceptance criteria

• Three defaults agree (removed has_hook entirely)
• Tier-1 quickstart gets working compaction without editing policy source
• Inert policy is discoverable without reading a reason string (warning logged)
• Host capability is not in governance record
• docs/policies/context_compaction.md states where hook comes from

Behaviour change

Anyone relying on context_compaction being silently inert will now get working compaction (prompts rewritten). This is the fix, not a regression — documented in changelog.

Non-scope

• _compact_messages quality (only reachability matters here)
• Streaming path (wrap_stream at :391) — issue Multimodal stream governance: implement wrap_stream and time-windowed accrual (spec) #110's territory

[tishachawla-jg]

Hi @RjyavardhanSingh, can you please resolve the conflicts also examples/config/default.yaml also swaps model: gpt-4o-mini → gemini-2.0-flash in 5 places while keeping provider: openai. That's unrelated to this fix and an inconsistent config (OpenAI provider + Gemini model won't resolve), looks like a local-testing artifact. Could you revert those 5 lines?

[RjyavardhanSingh]

@tishachawla-jg Got it, will fix both unning ruff format on context_compaction.py and reverting the gemini model changes in examples/config/default.yaml. Should be ready shortly. i had changed that for local testing but forgot to restore my bad sorry for that