Add reviewed governed-source channel adapters without implicit credential reuse

[AjnasNB]

Context

Maqam 0.3.0 adds provider-neutral governed source routing, normalized research documents, bounded host-defined checks, RSS/Atom parsing, and a feed-aware HTTP crawler. Agent Reach demonstrates the usefulness of broad, explicit source-channel setup and diagnostics, but Maqam deliberately does not copy its automatic installation, browser-cookie/session reuse, login helpers, or platform-specific command wrappers.

This issue tracks future breadth as small reviewed adapters, not a promise of Agent Reach feature parity.

Scope

Add one provider or upstream capability per pull request behind a static ResearchSourceAdapter and a registered ToolGateway tool. Start with public, read-only sources that need no login. Authenticated sources require a separate threat model and explicit allowAuthenticated: true behavior.

Acceptance criteria for each adapter

• host-supplied client or reader; no implicit network, shell, package installation, cookie extraction, or login
• deterministic offline fixture requiring no account, key, model call, network request, or external side effect
• allow case dispatches exactly once through the registered Maqam tool identity
• policy, approval, authentication, authorization, malformed output, robots/security, and unknown failures dispatch no fallback
• only explicit ResearchSourceUnavailableError permits ordered fallback
• normalized documents record adapter, channel, retrieval time, source URI, and bounded provenance
• doctor status states exactly what was checked and supports cooperative cancellation
• Node 20, 22, and 24 CI coverage
• license/provenance review for every upstream dependency or snippet
• documentation names direct-call bypasses, credential ownership, rate limits, data handling, and unsupported behavior
• no partnership, certification, universal-governance, anti-bot, or parity claim

Candidate sequence

1. Public GitHub repository/issue reader fixture using a host-supplied client.
2. Public feed/search adapter example with explicit request budgets.
3. Provider-specific authenticated designs only after security review.

Related: #8 covers the separate offline Google ADK FunctionTool contract fixture.

[AjnasNB]

Implementation direction after the 0.3 governed-source foundation:

• Model every channel as an ordered backend set with a real health probe, selected-backend explanation, and repair recipe.
• Keep credential classes explicit: anonymous-public, local-process, browser-session, and developer-credential. Never silently fall through from one class to another.
• Preserve ResearchSourceRegistry -> ToolGateway -> PolicyEngine -> trace/evidence for every selected backend; no direct channel bypasses.
• Ship anonymous-public coverage first: bounded webpage reads, hosted no-key search, public YouTube metadata/available captions, RSS/Atom, and public GitHub records.
• Treat authenticated X/Reddit/LinkedIn/social routes as a separate local session-broker milestone with opt-in browser-profile selection, dedicated-account guidance, origin allowlists, revocation, redaction, and no raw-cookie export by default.
• Add per-channel terms/rate-limit/privacy metadata and fail closed for login, paywall, consent, geographic, age, or automation restrictions.
• Add a cross-platform maqam sources doctor --live mode that is opt-in, spends a tiny bounded probe budget, distinguishes configured vs actually reachable, and outputs machine-readable remediation.
• Add deterministic fallback tests proving that policy denial, approval failure, authentication failure, and security rejection are fatal; only explicit availability failures may try the next backend.

The release claim should stay narrow: selected governed public research, not unrestricted or universal internet access.

[AjnasNB]

A narrow browser-agent interoperability fixture is now tracked in #31. That issue covers offline Page Agent-style proposal → Maqam structural-plan translation only; it does not claim upstream code is incorporated or permit natural-language tasks to dispatch browser writes directly.