feat: route compaction server through backend lifecycle

[danielcherubini]

Summary

Route the compaction server through the existing backend lifecycle (Kokoro TTS pattern) instead of custom subprocess management. This unifies compaction with the shared ModelState lifecycle (Starting → Ready/Failed) for spawn, health poll, reaping, and auto-restart.

Changes

• BackendType::Compaction — New enum variant with is_non_inference_backend() helper
• CompactionConfig cleanup — Renamed timeout_ms → request_timeout_ms for clarity
• load_compaction_backend() — New lifecycle method using model registry (Starting → Ready/Failed)
• Compaction handler rewrite — Uses ensure_compaction_backend() via model registry instead of custom CompactionServerState
• Shared helpers — Extracted get_backend_url() to handlers/helpers.rs (shared with TTS)
• Delete custom lifecycle — Removed CompactionServerState enum, compaction_server field, and 3 custom lifecycle methods (~362 lines deleted)
• Skip compaction in idle/LRU — check_idle_timeouts() and evict_lru_if_needed() exclude compaction backend
• Bug fix — evict_lru_if_needed() now checks runtime models map (not just DB configs) to exclude non-inference backends

Commits

• e332549 feat: add BackendType::Compaction and is_non_inference_backend helper
• f3d2d89 refactor: rename timeout_ms to request_timeout_ms in CompactionConfig
• 234466f feat: add load_compaction_backend using model registry lifecycle
• e7fcb4e refactor: rewrite compaction handler to use model registry
• 3c821f9 refactor: remove custom compaction lifecycle, use model registry
• 5bf1c9f fix: verify web API round-trip for compaction config
• 48d086f fix: exclude compaction from LRU eviction via runtime models map
• 11aa9c9 refactor: remove redundant health_ok guard in load_compaction_backend

Test plan

• cargo check --workspace — clean
• cargo clippy --workspace -- -D warnings — clean
• cargo test --workspace — 851 tests pass
• Manual test: enable compaction in config, verify it starts via model registry
• Manual test: verify compaction is not evicted by LRU
• Manual test: verify compaction survives proxy restart

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ℹ️ Review info

⚙️ Run configuration

Configuration used: Organization UI

Review profile: CHILL

Plan: Pro

Run ID: 6bf35314-2044-4a41-8d03-ebfa81bf2937

📥 Commits

Reviewing files that changed from the base of the PR and between e17cd25 and 5f3e883.

📒 Files selected for processing (18)

• crates/tama-cli/src/commands/backend/install.rs
• crates/tama-cli/src/commands/backend/update.rs
• crates/tama-core/src/backends/installer/urls.rs
• crates/tama-core/src/backends/types.rs
• crates/tama-core/src/backends/updater.rs
• crates/tama-core/src/config/types.rs
• crates/tama-core/src/proxy/handlers/compaction.rs
• crates/tama-core/src/proxy/handlers/helpers.rs
• crates/tama-core/src/proxy/handlers/mod.rs
• crates/tama-core/src/proxy/handlers/tts.rs
• crates/tama-core/src/proxy/lifecycle/mod.rs
• crates/tama-core/src/proxy/state.rs
• crates/tama-core/src/proxy/types.rs
• crates/tama-core/src/updates/checker.rs
• crates/tama-web/src/api/backends/types.rs
• crates/tama-web/src/pages/config_editor.rs
• crates/tama-web/src/types/config.rs
• docs/plans/README.md

✨ Finishing Touches

🧪 Generate unit tests (beta)

• Create PR with unit tests
• Commit unit tests in branch feature/compaction-backend-lifecycle

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