[Meta] DevTools suite — one product from visualizer, time-travel, tracing, profiling

[pathosDev]

Coordination umbrella — no new feature scope of its own; it makes five existing tickets ship as one product instead of five bolt-ons.

Rationale

Erlang's observer is a big part of why the BEAM feels magical: you can see the system. We have five separate tickets pointing at the same outcome — #204 (live cluster visualizer), #217 (dev-mode tracing visualizer), #218 (per-actor explain-plan), #201 (time-travel debugger over the journal), #226 (flame-graph profiler). Built independently they would each invent their own event tap and UI shell.

Scope (architecture clamp)

• One introspection tap: a versioned protocol over the existing management endpoints + an EventStream/journal tap that all five features share (actor tree, message-flow samples, mailbox depths, shard/cluster topology, journal cursors).
• One embeddable web UI shell (DevTools.attach(system, { port })) hosting the features as panels.
• Constraint (dependency policy): the UI ships build-time bundled / vanilla — no UI framework or asset appears as a runtime dependency of the package; no CDN loads.
• Sequencing: [Feature] Live cluster visualizer (shipped in package) #204 (visualizer panel) → [Feature] Dev-mode tracing visualizer (Flame-graph of message flows) #217/[Feature] Per-actor explain-plan (last-N message timing breakdown) #218 (tracing + explain-plan) → [Feature] Time-travel debugger over journal #201 (time-travel, journal-backed) → [Feature] In-process actor flame-graph profiler #226 (flame graph). Replay integration points to [Feature] Deterministic Simulation Testing (FoundationDB-style) #200 (deterministic simulation).

import { DevTools } from 'actor-ts/devtools';
DevTools.attach(system, { port: 9333 });
// http://localhost:9333 — live actor tree, message flow, mailbox depths; later time-travel (#201)

Documentation

DevTools docs chapter (EN + DE) grows with each panel; CHANGELOG per landed panel.

Acceptance (umbrella)

• Shared tap protocol documented + versioned before the first panel merges; each panel issue references and reuses it; "./devtools" subpath export.

Relates

Tracks: #204, #217, #218, #201, #226. Feeds on #196 (mailbox metrics), #200 (simulation). Dependency policy #419. Improvement program M6.