feat(backends): add experimental herdr-core runtime backend

.agents/skills/harness-adapters/references/harness/commandcode.md

@@ -33,7 +33,7 @@ Command Code draws a bare `❯` composer between two rules, parks the terminal c
 Its `Ask your question...` placeholder is truecolor bright enough to survive the fleet ghost ceiling, so `../../../bin/fm-composer-lib.sh` reads a screen with a Command Code identity at a higher ceiling; typed text is the default foreground and stays pending.
 The launch clears `NO_COLOR` and pins `COLORTERM=truecolor`, because a 256-colour terminal renders the placeholder in an untested palette colour.
 `../../../bin/fm-tmux-lib.sh` supplies the `commandcode` identity on tmux, while Herdr's native detection reports `cmd`.
-Zellij, cmux, and orca supply no such identity, so the placeholder would read pending there and `../../../bin/fm-spawn.sh` refuses a Command Code launch on those backends.
+Zellij, cmux, orca, and herdr-core supply no such identity, so the placeholder would read pending there and `../../../bin/fm-spawn.sh` refuses a Command Code launch on those backends.
 The delivery busy signals are `esc to interrupt` and the bullet-framed elapsed cell on the status row.
 
 ## Primary integration

.agents/skills/stuck-crewmate-recovery/SKILL.md

@@ -35,13 +35,13 @@ Read the targeted current state with `bin/fm-crew-state.sh <id>` before deciding
 A no-mistakes run matched to the crew's branch and current code remains authoritative when the endpoint is dead: handle a terminal or parked run through the normal lifecycle, and keep supervising an active run instead of creating a duplicate worker.
 
 When no authoritative run accounts for the task, inspect only its recorded backend and worktree inventory.
-Use `treehouse status` for treehouse-backed tmux, herdr, zellij, or cmux tasks, and use the recorded `orca_worktree_id=` and `terminal=` for Orca tasks.
+Use `treehouse status` for treehouse-backed tmux, herdr, zellij, cmux, or herdr-core tasks, and use the recorded `orca_worktree_id=` and `terminal=` for Orca tasks.
 Do not sweep another home's endpoints or infer ownership from a matching window label.
 
 Before relaunch, prove that no live agent still owns the recorded task and that the existing worktree remains available.
 Preserve its uncommitted changes and commits, keep the same task identity, and resume or relaunch the recorded harness in that existing worktree with the same brief plus a concise progress note.
-A HERDR endpoint that is not merely idle but destroyed - a pane or workspace removed in Herdr churn - is recovered by that same relaunch, which creates one fresh endpoint in the existing worktree and rebinds the task's record to it; nothing special is needed, and the worktree is untouched ([`docs/agent-control.md`](../../../docs/agent-control.md) "Reclaiming a task whose endpoint is gone").
-That relaunch proves the endpoint is destroyed before it rebinds, so a Herdr server that was merely stopped is adopted back rather than duplicated.
+A Herdr or herdr-core endpoint that is not merely idle but destroyed is recovered by that same relaunch, which creates one fresh endpoint in the existing worktree and rebinds the task's record to it; nothing special is needed, and the worktree is untouched ([`docs/agent-control.md`](../../../docs/agent-control.md) "Reclaiming a task whose endpoint is gone").
+That relaunch proves the endpoint is destroyed before it rebinds, so a merely stopped Herdr server is adopted back rather than duplicated, while a stopped herdr-core core's non-kept terminal is re-created.
 On tmux there is no reclaim: a task record carries no socket identity for its endpoint, so a `missing` window cannot be told apart from one on a tmux server this seat cannot address, and both `exit` and `relaunch` refuse.
 Do not work around either refusal by respawning - it means a live agent may still hold that worktree.
 That reclaim is the owning home's operation only, and a secondmate is the one exception: recover it through `bin/fm-spawn.sh <id> --secondmate` as above.

README.md

@@ -226,6 +226,7 @@ Firstmate's skills live in two separate places with different audiences:
 - [docs/zellij-backend.md](docs/zellij-backend.md) - current setup and limits for the experimental Zellij backend.
 - [docs/orca-backend.md](docs/orca-backend.md) - current setup and limits for the experimental Orca backend.
 - [docs/cmux-backend.md](docs/cmux-backend.md) - current setup, socket security, and limits for the experimental cmux backend.
+- [docs/herdr-core-backend.md](docs/herdr-core-backend.md) - current setup, detection, and limits for the experimental herdr-core backend.
 - [docs/codex-app-backend.md](docs/codex-app-backend.md) - the current blocked Codex App backend boundary and rollout contract.
 - [docs/verification/runtime-backends.md](docs/verification/runtime-backends.md) - active maintainer verification for runtime backend guarantees.
 - [docs/gerrit-forge-integration.md](docs/gerrit-forge-integration.md) - maintainer architecture for the forge axis: why change-shaped review is not a forge variant, the mode/forge/shape composition test, and where responsibility for forge mechanics sits.