docs: record architecture decisions (ADR-0001..0009) and operations knowledge

Add docs/adr/ with a chronological ADR set reconstructed from the project
history (no orchestrator, one storage format, derived-state sync,
SQL-over-SSH contract, WireGuard beneath SSH, IaC boundaries, non-root
image, runtime data paths, bounded lake scans), an index README, and a
template. Distinguish repo-local ADRs from ecosystem-wide ASRs.

Expand AGENTS.md with a decision-records section and a runtime/operations
guide (service URLs, rebuild workflow, CPU budget knobs). Reference the
ADRs from README, CONTRIBUTING, and the affected design docs, and add an
open question for T1 partition pruning.

docs/adr/README.md

@@ -0,0 +1,40 @@
+# Architecture Decision Records
+
+This directory records the significant decisions behind Swarm House, in the
+order they were made. Each record is immutable once **Accepted** — a later
+decision that changes course gets a new number and supersedes the old one
+rather than editing it.
+
+## ADR vs ASR
+
+| Kind | What it captures | Where it lives |
+| --- | --- | --- |
+| **ADR** (Architecture Decision Record) | A point-in-time decision for *this* repository, with the options considered and their consequences | Here, in `docs/adr/` |
+| **ASR** (Architecture Standard Record) | A standing, cross-repository policy every project must obey (Go-first, secrets, layout) | The ecosystem `inventar` repo, not here |
+
+The rules in [`../../AGENTS.md`](../../AGENTS.md) are this repo's local standing
+constraints; anything ecosystem-wide belongs in `inventar` as an ASR. Design
+decisions specific to the platform are ADRs and belong here.
+
+## Index
+
+| ADR | Decision | Status |
+| --- | --- | --- |
+| [ADR-0001](ADR-0001-no-swarm-orchestrator.md) | No swarm-wide orchestrator; coordinate through data | Accepted |
+| [ADR-0002](ADR-0002-one-storage-format.md) | One storage format on every tier — Parquet + DuckDB, Hive layout | Accepted |
+| [ADR-0003](ADR-0003-sync-derived-state-only.md) | Sync derived state only; raw telemetry stays local | Accepted |
+| [ADR-0004](ADR-0004-sql-over-ssh-contract.md) | Read-only SQL-over-SSH as the peer query contract; no debug API | Accepted |
+| [ADR-0005](ADR-0005-wireguard-beneath-ssh.md) | WireGuard beneath SSH for the mesh transport | Accepted |
+| [ADR-0006](ADR-0006-iac-boundaries.md) | IaC split: Ansible hosts, Terraform ground, Flux ground-only, fleet manifest for drones | Accepted |
+| [ADR-0007](ADR-0007-non-root-image.md) | Run the simulator image as a non-root user | Accepted |
+| [ADR-0008](ADR-0008-runtime-data-paths.md) | Shared `var/t1` / `var/t3` runtime paths; state out of Git | Accepted |
+| [ADR-0009](ADR-0009-bounded-lake-scans.md) | Bound observability lake scans to a flight window and cache | Accepted |
+
+## Writing a new ADR
+
+1. Copy [`TEMPLATE.md`](TEMPLATE.md) to `ADR-NNNN-short-slug.md` (next free number).
+2. Fill in Context, Options (if more than one was real), Decision, Consequences.
+3. Add a row to the index above.
+4. Cross-link the ADR from the design doc it affects (and vice versa).
+
+Keep the tone laconic: state the decision and why, skip the narrative.