refactor(coding-agent): extracted shared auto-backgrounding and job wait helpers

- Extract foreground wait, notice formatting, and settlement racing logic into a shared module.
- Update async job type definitions to support eval jobs alongside bash and task jobs.
- Add configuration settings for eval auto-background thresholds.

packages/coding-agent/CHANGELOG.md

@@ -11,6 +11,7 @@
 - Added `extendedContext` setting (`/settings` → Context → General, default on). When off, models with a premium long-context price tier (OpenAI GPT-5.6 Sol/Terra/Luna bill 2x input / 1.5x output above 272K input tokens, on both the API and subscription Codex) are capped at the standard-pricing threshold — they appear as 272K again and compaction fires before a request crosses into premium billing. Toggling mid-session re-clamps or restores the active model's window immediately. Anthropic Claude 4.6+ serves its full 1M window at standard pricing, so no Anthropic model is affected.
 - Added click-to-toggle and drag-to-reorder controls for list-valued `/settings` editors.
 - Added `compaction.asyncEnabled` (Async Compaction, default on): when context enters the band just below the compaction threshold, maintenance speculatively summarizes in the background off a branch snapshot (first configured LLM-backed method — remote, handoff, or soft — isolated from the live turn by a side session id) and holds the armed result; crossing the threshold then splices it in instantly instead of blocking on a summarization round-trip. Armed results are invalidated by branch changes, reset boundaries, model switches that strand provider-native replay payloads, and context growth past `keepRecentTokens` (which re-speculates). The status line pulses the auto-compact icon while a speculation runs and holds it in accent once a result is armed.
+- Added auto-backgrounding for eval cells, mirroring the bash policy: with `eval.autoBackground.enabled` (default off), a cell still running after `eval.autoBackground.thresholdMs` (default 60s) — or when a queued user/peer message steers mid-wait — converts into a background job that keeps executing on the kernel and delivers its result automatically. Both settings inherit the RPC-host default treatment alongside their bash counterparts.
 
 ### Changed
 
@@ -20,6 +21,7 @@
 - `/settings` rows can now carry a risk note: a warning glyph on the row plus a warning-colored line above the description. `External Thinking` (`externalThinking`, `--external-thinking`) is the first user — providers have flagged the request shape it produces as abuse, up to account-level enforcement, so both the settings entry and `--help` now say so.
 - The todo HUD header now draws a summed progress bar counting closed/total tasks across every stage. Once all tasks close, the bar smoothly collapses before the row disappears.
 - The todo HUD now carries overall progress in the tree spine instead of a horizontal header bar: the top-level connector column runs unbroken from the `TODO` header down the left edge and closes with a short `└────` elbow tail under the block. The closed/total fraction (summed across every stage) fills that path in accent — down the spine, around the bend, out along the tail. Once all tasks close, the accent smoothly drains back up before the header row disappears.
+- The todo HUD now carries overall progress in the tree spine instead of a horizontal header bar: the top-level connector column runs unbroken from the `TODO` header to the last row, and the closed/total fraction (summed across every stage) colors it top-down in accent. Once all tasks close, the accent smoothly drains out of the spine before the header row disappears.
 - Token counting is now scoped to the model being billed rather than to a process-global tokenizer: session maintenance, stats, advisors, `/context`, snapcompact inline imaging, and `compress` each count through the owning agent's `Tokenizer` (`agent.tokenizer`). Message counting is `Tokenizer.countMessage`/`countMessages` (replacing the free `estimateTokens(message, tokenizer)` helper; the legacy shim keeps a compat `estimateTokens` export for legacy pi extensions). `estimateToolSchemaTokens`, `estimateSkillsTokens`, `computeNonMessageTokens`, and `computeNonMessageBreakdown` take an explicit tokenizer; standalone prompt inspection intentionally keeps the default estimate because it has no resolved catalog model.
 - The advisor runtime's `maintainContext` hook now receives the pending update as a message instead of a pre-computed token count — sizing it needs the advisor model's tokenizer, which the host owns.
 - Handoff no longer starts a new session: `/handoff` and the auto-maintenance `handoff` method now commit the generated document as a regular compaction entry on the current session (document becomes the summary, recent history is kept per `compaction.keepRecentTokens`, session id/transcript/cache key unchanged). The `session_before_switch`/`session_switch` extension events no longer fire with reason `"handoff"`, mid-turn maintenance no longer skips the handoff preference, and overflow recovery can now apply a pre-armed handoff result.