ADR 0011: Adopt the isolated-worktree workflow for discern's own development

Amendments.

• Vocabulary: the retired product-category wording reads as discern, the gate, or the bar, and the older Recipe reference below describes the then-current command implementation (a Project Script surface today); the decision below — the worktree workflow as the way discern develops itself — is unchanged, though its mechanics have since moved on.
• ADR 0020: .discern/ is dissolved.
• ADR 0025: the db/dev_server seams became per-worktree resources.
• ADR 0040: the hooks parse their payload inside the binary rather than shelling out to bin/agent worktree lifecycle helpers.
• ADR 0052: placement is the configurable sibling default.

Status: accepted

ADR 0010 installed discern into this repo and made discern done the gate, but it deliberately deferred one piece: whether to develop discern inside discern's own isolated git worktrees. The SessionStart/WorktreeCreate/WorktreeRemove hooks shipped scaffolded but dormant, and the open question was parked in TODO.md.

Two things make the call easy now. First, the configuration is already in place: [worktree] enabled = true, with both adapter seams (db, dev_server) empty — which is exactly right for a Deno CLI that has no database and no dev-server, so a worktree round is pure git mechanics with nothing to clone or link. Second, the only real obstacle was portability: the WorktreeCreate/WorktreeRemove hook commands invoked zsh -c, which assumes a login shell that is absent on a stock Linux box and in CI. The hook bodies are already POSIX-clean, so moving them to sh -c removes the one thing standing between "scaffolded" and "usable".

Adopt the worktree workflow as the way discern is developed: each line of work gets its own isolated worktree under .claude/worktrees/, created and torn down by discern hooks.

• The hooks run under /bin/sh, not zsh. Both the root .claude/settings.json and the shipped templates/.claude/settings.json.tmpl now use sh -c; the command bodies were already portable. This is a straight portability fix that also benefits every downstream install, not just this repo, so it is not gated behind the adoption decision.
• No further configuration. [worktree] enabled = true and the empty db/dev_server adapters stay as they are; a worktree round for this repo is the git-and-gate path only.
• The SessionStart worktree ensure hook and the WorktreeCreate/WorktreeRemove hooks are now load-bearing, not dormant.

• Branch work is isolated by default: a worktree per line of work, its own checkout, no stomping on the main tree mid-session. This is the workflow the discern exists to provide, now exercised by its own author — the same validation argument as ADR 0010.
• The hooks are live, so a breakage in them now affects day-to-day development, not only downstream users. They stay deliberately thin (a few lines of POSIX sh that shell out to bin/agent worktree lifecycle helpers); the real logic lives in the engine recipes, which the test suite covers hermetically.
• port = true still derives a per-worktree port that nothing in this repo consumes (there is no dev-server). It is harmless and left on rather than carrying a special-case; a project that wires a dev-server adapter would want it.
• The TODO.md "decide whether to adopt" item is closed by this record.

• Keep developing on main directly. Simplest, but it leaves the most-distinctive part of discern unexercised by its own author and forgoes the isolation the tool is built to give. The dormant-hooks status quo was only ever meant to be temporary (ADR 0010 parked it in TODO.md); leaving it parked indefinitely is the non-decision this ADR exists to end.
• Enable the hooks but leave the choice informal. That is effectively the dormant state — live config, no committed practice — which is exactly what produced a lingering TODO item. Recording the decision is the point.