[P2][CONN-03] Protocol adapters and compatibility extraction

Programme: #1
Epic: #18

## Objective
Support multiple connector transports while preserving one internal capability/security model and a truthful degradation path when structured APIs are unavailable.

## Scope
- Official REST/GraphQL/provider SDK adapters.
- MCP client support with explicit tool/resource/schema mapping.
- WebMCP browser-resident adapter where pages expose structured tools.
- Feed/file/local-source adapters and domain-specific protocols.
- Authenticated DOM/accessibility extraction through WEB-03 as compatibility path.
- Bounded visual extraction only as a last-resort compatibility mode.
- Optional provider-supplied UI treated as untrusted content.

## Design rules
- Protocol/tool discovery never grants permission.
- MCP/WebMCP descriptions remain untrusted input.
- Provider-specific semantics and support limitations remain visible through the normalized interface.
- DOM/visual automation is not represented as equivalent reliability to an official API.

## Acceptance criteria
- [ ] Same logical resource/action can be represented through supported protocol adapters without bypassing the capability broker.
- [ ] Unsupported or lossy semantics fail visibly and can route to Original view.
- [ ] Malicious MCP/WebMCP metadata cannot widen authority or override task/system policy.
- [ ] DOM fallback records origin/account/source revision and verification limits.
- [ ] Visual fallback is explicitly marked lower-confidence/compatibility mode.
- [ ] Protocol-specific conformance fixtures cover disconnects, malformed schemas and version drift.

## Dependencies
- CONN-01
- WEB-03

**First phase:** P2
**Maturity target:** P5
**Owner:** connectors-domains

## Task issues
- [ ] #388 `CONN-03.T01` — Implement REST and GraphQL adapter primitives
- [ ] #389 `CONN-03.T02` — Implement MCP discovery and tool/resource mapping
- [ ] #390 `CONN-03.T03` — Implement browser-resident WebMCP integration
- [ ] #391 `CONN-03.T04` — Implement local files and feed adapters
- [ ] #392 `CONN-03.T05` — Implement semantic browser compatibility extraction
- [ ] #393 `CONN-03.T06` — Add bounded visual fallback and provider UI isolation
- [ ] #394 `CONN-03.T07` — Build per-protocol drift and disconnection tests

Start by reading dependencies CONN-01 and WEB-03, then select a concrete task issue from #388–#394 rather than implementing this umbrella issue directly. Use the acceptance criteria to verify capability-broker enforcement, visible lossiness, untrusted metadata handling, fallback provenance, and protocol conformance coverage.

Written by the indexing model from the issue text.