ADR 0009: one Werkator instance serves a set of repositories

Records the tenet revision and its shape: instance registry and
instance keys in ~/.werkator.yml (one instance per OS user), optional
repo defaults in an explicit defaults: block merged below every repo's
own layers, repo config unchanged in each repository, registry-wins
precedence, basename repo names. Rejected: a federation dashboard over
single-repo instances (keeps N services), and the status quo.
Konzept/AGENTS architecture wording changes only when the
implementation lands; the decision list carries 0009 now.

Co-Authored-By: Claude Fable 5 <noreply@anthropic.com>

docs/adrs/0009-2026-09-01.multi-repo-instance.md

@@ -0,0 +1,60 @@
+# One Werkator Instance Serves a Set of Repositories
+
+**Status:**
+- proposed: 2026-09-01
+- accepted: 2026-09-01
+- rejected: -
+- superseded: -
+
+**Decision [accepted]:** The founding tenet "one instance per repository" is revised to "one instance per repository *set*": a Werkator instance aggregates self-contained repositories listed in an instance registry, sharing one service, one port, one UI, one watcher schedule, and one global executor cap.
+Implementation is planned as `docs/plan/22-multi-repo.md`; this ADR records the decision and its shape, not the code.
+
+## Context and Problem Statement
+
+"One instance per repository" (docs/Werkator-Konzept.md) does not scale even to two repositories on a Hostsharing Managed Webspace: building Werkbaum next to Werkator on mih34 would need a second service, a second assigned port, a second tunnel or domain, a second UI and metrics page.
+Every repository multiplies operations while the instance-level resources could be shared.
+
+### Technical Background
+
+Everything repository-specific already lives inside the repository or is keyed by it: machine config with secrets, build results, auto-build slots, worktrees, and buildenvs under `.git/werkator/`; the artifact store under a per-repo key.
+An instance can therefore aggregate repositories without absorbing their state — adding or removing a repository is a registry entry, never a data migration, and single-repo mode stays the degenerate case (a registry of one, implicitly the current working directory).
+
+## Considered Options
+
+* One instance per repository set (registry + aggregation) — chosen
+* A federation dashboard proxying several single-repo instances
+* Status quo: one instance, one repository
+
+### One Instance per Repository Set
+
+Good:
+
+- One service, port, UI, tunnel/domain, metrics page for any number of repositories.
+- Repositories stay self-contained; per-repo secrets, history, and pinning semantics are untouched.
+- Global concurrency control across all repositories.
+
+Bad:
+
+- The repo dimension must be threaded through executor pools, watcher cycle, routes, and UI — the largest refactor since the rewrite (mitigated by a behavior-preserving `RepoContext` session first).
+- Instance-level and repo-level configuration must be split cleanly (see below).
+
+### Federation Dashboard over Single-Repo Instances
+
+Rejected: less invasive, but it keeps N services, N ports, and N tunnels — it solves only the UI aggregation, not the operations burden that motivated the change.
+
+### Status Quo
+
+Rejected: on a webspace, ports and domains are the scarce, manually assigned resource; per-repository services do not scale there.
+
+## Decision Outcome
+
+One instance per repository set, with the configuration split decided 2026-09-01:
+
+- **Instance config** lives in `~/.werkator.yml` in the home directory of the user running the instance — one instance per OS user, matching the platform model. It carries `server.*` (port, domain/public base URL, nginx), the repository registry, the control token, the global `executor.maxConcurrent`, and the watcher schedule. The file name stays `.werkator.yml` in all three locations; the location carries the meaning.
+- **Repo defaults** may live in the home file, but only in an explicit `defaults:` block, merged *below* every repository's own layers (home defaults → committed project config → repo machine config → branch layer); pinning semantics are unchanged. Accepted cost: secrets may then live in two places.
+- **Repo config** stays in each repository: the committed `.werkator.yml` and the machine config in its `.git/werkator/`.
+- Instance keys found in a repo's machine config are ignored with a warning naming both files once a home config exists — never merged silently.
+- When a home config with a registry exists, `werkator server` serves the registry regardless of the current directory; without one it serves the current directory exactly as before.
+- Repository names (routes, UI) default to the directory basename, are overridable per registry entry, and duplicates abort the start loudly.
+
+Consequences: `docs/Werkator-Konzept.md` and AGENTS.md change their wording when the implementation lands (plan step 22 sessions B–D); until then this ADR documents the target and the existing behavior remains accurate.

docs/plan/22-multi-repo.md

@@ -38,14 +38,13 @@ The pinning model is untouched: pinned keys still come from each repo's machine
 
 ### A — Decision and schema (ADR 0009)
 
-- Write ADR 0009: revise the one-instance-per-repository tenet to one-instance-per-*set*; record the aggregator idea and the key ownership split above.
-  Considered alternative to record: a federation dashboard proxying several single-repo instances — less invasive, but it keeps N services/ports and solves only the UI, not the operations burden.
+- ~~Write ADR 0009~~ — done 2026-09-01: `docs/adrs/0009-2026-09-01.multi-repo-instance.md` revises the one-instance-per-repository tenet to one-instance-per-*set* and records the aggregator idea, the key ownership split, the four 2026-09-01 decisions, and the rejected federation-dashboard alternative.
 - Define the instance config: `~/.werkator.yml` (decided 2026-09-01) — the repository registry plus the instance-level keys above; one instance per OS user, which matches the platform model (pac users on a webspace, service users elsewhere).
   `werkator server` without a home config serves the current directory exactly as today.
 - Decide the transition for instance keys that today sit in a repo's machine config (mih34's carries `server.*`): once a home config exists, repo-level instance keys are ignored with a warning naming both files — never merged silently.
 - Repo identity for display and routes (decided 2026-09-01): a short unique name per registry entry, defaulting to the repository's directory basename, overridable in the entry; duplicate resulting names abort the start loudly. Used as the route segment (`/repos/<name>/…`) and UI grouping key.
 - Precedence (decided 2026-09-01): when a home config with a registry exists, `werkator server` serves the registry regardless of the current directory — one user, one instance, deterministic; without a home config it serves the current directory exactly as today.
-- Update `docs/Werkator-Konzept.md` and AGENTS.md wording ("one instance per repository set").
+- Update `docs/Werkator-Konzept.md` and the AGENTS.md architecture wording ("one instance per repository set") when the implementation lands (sessions B–D) — until then the existing behavior description remains accurate; the AGENTS.md decision list carries ADR 0009 already.
 
 ### B — RepoContext refactor, behavior unchanged
 
@@ -80,7 +79,7 @@ The pinning model is untouched: pinned keys still come from each repo's machine
 
 ## Acceptance Criteria
 
-- Session A: ADR 0009 merged; registry and key-ownership documented in `docs/configuration.md`.
+- Session A: ADR 0009 written (done 2026-09-01); the registry and key ownership land in `docs/configuration.md` together with the implementing sessions, since that reference describes implemented configuration only.
 - Session B: full suite green with `RepoContext` threaded through; no route or behavior change observable.
 - Session C: an instance with two registered repos builds pushes in both, with per-repo error isolation proven by a test (one broken origin, the other keeps building).
 - Session D: both repos browsable in one UI; single-repo installations keep their existing URLs.