Revises the 2026-06 devexp tech spec to match the spec-owner review (comments on the deployed spec + the Ideal User Flow Excalidraw + four clarifying answers). These reverse several load-bearing decisions, so the change touches all spec files plus the index.

Four reversals applied across the spec

1. Config back in files. A worker ships its own defaults.yaml; worker-compose.<target>.yaml carries per-worker config: overrides (effective = defaults.yaml ◁ compose base ◁ target). The configuration worker is now optional and acts as a read/update layer over the active compose file (never edits defaults.yaml, errors when no compose file is found). iii runs with zero workers, including no configuration worker. (Reverses "no config in any file / mandatory store.")
2. Multi-host hub. The engine manages nothing and reports availability via a new worker_available trigger; depends_on (including on remote workers) gates by subscribing to it. iii-process-daemon is the local runner's supervisor (one option beside docker/systemd/bash), not the universal owner of every PID. Cross-host lifecycle management is not a v1 promise; fleet-scale stays iii Cloud. (Reverses "daemon parents every PID / multi-host out of scope.")
3. CLI surface. iii worker compose … is canonical; iii --compose is the tutorial one-liner (engine + compose up); the top-level iii up/iii down/iii ps/iii logs aliases are dropped. Adds iii trigger --timeout <secs|Inf>, console-as-worker (trigger::console), sandbox-via-trigger, and the iii worker --help/array-args/always-reinstall/--address fixes.
4. Onboarding journey added to lifecycle-and-onboarding.md: interactive "Welcome to iii!" tutorial, email capture → Mailmodo sequence, PostHog activation tracking, CI-verifiable tutorials.

Smaller corrections folded in

• depends_on name:/id: forms + trigger-gated, targeted (math→state, caller→http) readiness.
• iii.lock is local to each worker-compose.yaml (one lock per compose file).
• Retry with capped exponential backoff; timeouts may be set to Inf.
• Per-target sections (targets: and/or worker-compose.<target>.yaml).
• worker-compose.yml → worker-compose.yaml throughout.
• Adds the source Ideal User Flow.excalidraw.

Open points flagged for review

• defaults.yaml is introduced as a separate per-worker file from iii.worker.yaml (config defaults vs start/runtime manifest). If they should be merged, that's a follow-up.
• Targets are supported two ways (in-file targets: and separate worker-compose.<target>.yaml); narrow to one if preferred.
• Worker id kept as configuration, with config-worker:<id> as the addressing scheme/alias (the Excalidraw writes depends_on: - config-worker).
• Legacy em-dashes in untouched prose were left as-is (a full strip would be a noise-only diff); can be done as a separate pass.

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