> For the complete documentation index, see [llms.txt](https://docs.thecolliery.org/llms.txt). Markdown versions of documentation pages are available by appending `.md` to page URLs; this page is available as [Markdown](https://docs.thecolliery.org/benchmarks/coalhearth/readme.md).

# CoalHearth—interruption damage

> **What this measures, honestly.** CoalHearth journals session state so an interrupted session (limit-hit, crash) RESUMES instead of restarting cold. This benchmark quantifies the **damage a cold restart pays that a warm resume avoids**—on a mid-task interruption with a known-correct completion. It does **NOT** claim CH recovers lost in-flight compute (it does not—Incident E scope: it records that a spawned worker existed + its residue path, never its result).

## Two arms, one interruption

A 10-file refactor (rename `getUserData` → `fetchUserProfile`, update every reference) is interrupted **6 of 10 steps in**: the definition + 5 call sites are done; 4 references remain (2 call sites, a test, and a stale doc-comment—the last is a non-import ref that is easy to skim past). Fixture: `fixtures/refactor-midway/`.

* **COLD** (no CH)—an agent is handed the working tree with **no record of what was done** and must reconstruct state by re-scanning all 10 files, then finish.
* **WARM** (CH)—the same agent is handed CH's **recovery block** (what's done, what's modified, what remains, any in-flight agents) + only the remaining files, then finishes.

Scored: (a) **correctness**—did it find all 4 remaining refs, redo none of the 6 done? (b) **tokens**—`subagent_tokens` per arm. (c) **state fidelity**—what CH's real lib (`lib/state-snapshot.js`) reconstructs vs what a cold restart can.

## Honest scope

The token arm is engine- and scale-sensitive: on a small tree the per-agent baseline dominates and a strong model reconstructs state unaided, so the token delta is tiny—CH's token value is a **large-session** effect (re-scanning a big repo to reconstruct state is what costs). The **fidelity** arm is the categorical one: the in-flight-agent record has **no tree signal**, so a cold restart recovers 0% of it at any scale. See [`RESULTS.md`](/benchmarks/coalhearth/readme/results.md). **CC-only measurement so far**—CH now also ports to Antigravity 2.0 and five other config-only hook platforms, but no cross-platform arm has been measured yet.


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