Land leftover TUI polish (#549) and native Anthropic output_config (#550)

[justrach]

Closes leftover TUI polish (#549) and the Anthropic native schema carrier (#550). Both issues are closed; this PR is the remaining land on main.

#549 leftovers

• GRAFF_MCP_CONFIG wholesale off-switch. An existing, valid, empty override ({"mcpServers":{}}) no longer merges the project .mcp.json or plugin trees, so a pty/harness empty file does not trigger the trust prompt. A populated override still merges. A missing or invalid override is not an off-switch. /mcp trust and graff mcp list use the same rule.
• A full inbuf makes readStdin() return 0 and the loop kills the TUI as a phantom hangup #517 is run_stall.clearFullWedge with a unit test. The loop calls the helper instead of inlining pending_len == inbuf.len.
• TUI raw mode leaves IEXTEN and IXON set: the advertised Ctrl+V never reaches the app and Ctrl+S freezes the whole TUI #523 mutates a termios-shaped value and asserts IEXTEN/IXON (and the other raw bits) are clear. No more @embedFile greps for those flags.
• Clipboard banner was already gone on main (Ctrl+V lives in the footer). Panic restore was already restore.Panic.

#550 Anthropic native schema (formatting turn only)

On provider id anthropic, the tools-off formatting turn now sends

output_config.format = {type: "json_schema", schema}

minimax / kimi-anthropic stay on the structured_output tool. A rejection that mentions output_config (or response_format) sets the same sox_json_object quirk flag and retries in tool mode.

ADR 0001 is unchanged: no schema grammar on a tools-using turn. The spec kernel, Lean model, and Zig conformance cells were ratcheted (outputConfig carrier; anthropic tools turns may be silent because the two-phase split holds the schema).

Verification

scripts/eval-tier1.sh green: fmt, 600-line ceiling, spec fixtures, reachability, zig build, 1726 unit tests, 449 TUI tests, 17 PTY probes, invariants, SDK sync.

Left open

• TUI engine-substrate divergences: glyph-scraping, dropped events, label-only /plan & /strict, ungated !cmd (audit, 25 findings) #551 — six majors already on main; still the tracker for ~18 smaller drifts
• Experiment filesystems: pre-provision worktrees and fan out by default #629 — first slice shipped; forced fan-out / worktree list / deliver-back still open
• Distribute graff via the ACP Registry (agentclientprotocol/registry) #613 — registry listing + authMethods still blocking
• TUI audit triage: 16 unverified findings from the out-of-the-box review #524 / TUI escape/death audit round 2: 12 unverified findings #537 — leftover unverified TUI audit items