ARIA snapshot tool (stable role/name tree, Playwright aria-snapshot parity)

[ChrisRoyse]

Parent: #1192 (master #1063).

What

Emit a Playwright-compatible ARIA snapshot (YAML-like role: name tree) for the page or a subtree, with stable ordering, usable for diffing/assertions. Builds on the existing AX tree.

Where

New crates/synapse-mcp/src/server/browser_assert.rs merged in server.rs; AX mapping in cdp_dom.rs.

Done when (FSV)

• Snapshot role/name tree matches an independent AX dump of the same subtree.
• Ordering is stable across runs.
• Subtree scoping by element id works.

[ChrisRoyse]

Carry-forward directive - remove foreground-protection limiting, preserve 50+ foreground-capable lanes

This issue inherits the current operator direction recorded on #1223: #1223 (comment)

• Do not create, continue, revive, merge, depend on, or reintroduce foreground protection, background-only, broad foreground-denial, or capability-suppressing limiter policy/implementation under another name.
• Rework any code, docs, profile, tool description, prompt, policy, branch/worktree state, or product behavior that strands valid foreground or foreground-equivalent agent work.
• Target behavior is 50+ concurrent agents: use background/target-scoped routes when sufficient, and foreground-equivalent lanes/routes whenever valid work requires foreground semantics.
• Keep human_os_foreground separate from each agent's agent_logical_foreground / foreground_lane / owned target. Raw real OS foreground is a leased singleton break-glass path only, not the concurrency mechanism.
• Tool exposure is system behavior. Steer agents to intent-level routers and lane-aware routes without suppressing reachable foreground-equivalent capability.
• Browser work must use the already-open authenticated Windows Chrome session; do not launch new Chrome browser processes for browser work.
• Synapse behavior acceptance must use real wired Synapse MCP tool calls plus separate physical Source-of-Truth readback when a tool surface exists. Supporting scripts/tests/checks/builds are regression evidence only, never FSV.
• In this single-agent repo run, stale claimed, status:in-progress, or old agent labels are historical/resumable state, not another active Synapse repo agent.
• Issue-close hygiene remains mandatory: implementation commit/push before close when code changed, evidence/readback before close, then close-marker commit/comment. Commits include [skip ci].

Context-only comment; implementation and manual FSV remain on the issue itself.