Dart SDK: full parity with TypeScript Morph API Client

[cemal-yilmaz-bt]

Goal

Deliver a Dart/Flutter Morph API Client with functional parity to the existing TypeScript implementation (packages/core, packages/oauth2, packages/browser-storage, packages/logger): same JSON configuration schema, same OAuth2 / multi-context token lifecycle, HTTP pipeline behavior (auth resolution, retry, trace, 401 recovery), and plugin composition (provides / requires, provideAuth / provideStorage, logger chaining).

Foundation: Phase 1 scaffold in packages/dart/morph_core (#1, base branch f/plugin).

References:

• docs/architecture.md
• docs/api-reference.md
• docs/configuration.md
• docs/platform-adapters.md
• docs/token-lifecycle.md

Scope (parity targets)

TS package	Dart target (name TBD in PRs; split like TS)	Feature parity checklist
@morph/core	morph_core (expand scaffold)	MorphClient, MorphRuntime-equivalent, MorphConfig validation/interpolation, HostPipeline, HostClient, AuthHandle, errors, HTTP trace events, plugin topo-sort + MorphPluginContext
@morph/oauth2	e.g. morph_oauth2	AuthPlugin, TokenLifecycle, TokenVault, OAuth helpers, refresh / exchange / 401 recovery behavior aligned with token-lifecycle.md
@morph/browser-storage	e.g. morph_secure_storage or VM-first	StorageProvider; Flutter: secure storage / memory paths per platform-adapters.md
@morph/logger	packaged or nested	Optional logger plugin chaining onLog / onHttpTrace like TS

Non-functional: idiomatic Dart (snake_case public APIs, Future/streams where async), deterministic tests mirroring TS test intent where configs align.

Out of scope (unless explicitly expanded)

• Changing the canonical JSON schema consumed by TS (Dart must validate against the same semantics; schema evolution stays coordinated).
• UI samples (optional follow-up PoC); this issue tracks SDK parity first.

Acceptance criteria

• dart analyze and dart test pass for every shipped Dart package in CI (extend .github/workflows/dart.yml or split jobs per package).
• MorphClient.init with real config + @morph/oauth2-parity + storage plugin can obtain tokens and execute authenticated host requests (VM or Flutter test harness), behavior consistent with documented TS flows.
• Docs: docs/dart-parity.md updated when parity milestones land; parity matrix references TS APIs.
• Regression parity: Critical paths covered by tests analogous to TS (fixture JSON configs where shared).

Suggested sequencing (milestones inside this issue)

1. Typed MorphConfig / MorphOptions + validators + interpolate variables (Dart).
2. Runtime + plugins equivalent to TS MorphRuntime, runtime.ts.
3. OAuth2 package parity (TokenLifecycle, vault, OAuth URL/callback helpers).
4. Storage plugins (VM then Flutter secure storage adapters).
5. Logger plugin parity.
6. Integration / gold tests against same sample config files as TS (where practical).

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Blocked by / related: #1 (scaffold + CI entry point).

Branch policy: Deliver against f/plugin unless release policy moves default branch.