opentui(phase3): launcher integration — HERMES_TUI_ENGINE dual-engine

hermes --tui launches the native OpenTUI engine (Bun) when
HERMES_TUI_ENGINE=opentui (env) or display.tui_engine=opentui (config);
Ink stays the default and the shipping path is untouched.

- _resolve_tui_engine() (env > config > ink); refuses opentui on
  Windows/Termux (no Bun) -> falls back to ink with a notice.
- _make_opentui_argv() -> [bun, src/entry.real.tsx] (no build step).
- _bun_bin() with HERMES_BUN override.
- Branch at top of _make_tui_argv BEFORE _ensure_tui_node (Bun-only host
  must not bootstrap Node).
- Gate _launch_tui NODE_OPTIONS/--max-old-space-size on engine==ink (Bun
  is JSC; the V8 flag errors/ignores).

Verified end-to-end via tmux: real hermes --tui -> Bun -> OpenTUI ->
real Python gateway streamed a real reply. No-flag default still ink.

agent/model_metadata.py

@@ -141,8 +141,6 @@ DEFAULT_CONTEXT_LENGTHS = {
     # fuzzy-match collisions (e.g. "anthropic/claude-sonnet-4" is a
     # substring of "anthropic/claude-sonnet-4.6").
     # OpenRouter-prefixed models resolve via OpenRouter live API or models.dev.
-    "claude-fable-5": 1000000,
-    "claude-fable": 1000000,
     "claude-opus-4-8": 1000000,
     "claude-opus-4.8": 1000000,
     "claude-opus-4-7": 1000000,
@@ -970,16 +968,6 @@ def parse_available_output_tokens_from_error(error_msg: str) -> Optional[int]:
         # OpenRouter/Nous phrasing of the same condition.
         "in the output" in error_lower
         and "maximum context length" in error_lower
-    ) or (
-        # LM Studio / llama.cpp / some OpenAI-compatible servers:
-        #   "This model's maximum context length is 65536 tokens. However, you
-        #    requested 65536 output tokens and your prompt contains 77409
-        #    characters ..."
-        # The "requested N output tokens" phrasing means the OUTPUT cap is the
-        # problem (the input itself fits) — reduce max_tokens, don't compress.
-        "maximum context length" in error_lower
-        and "requested" in error_lower
-        and "output tokens" in error_lower
     )
     if not is_output_cap_error:
         return None
@@ -1011,22 +999,6 @@ def parse_available_output_tokens_from_error(error_msg: str) -> Optional[int]:
         if _available >= 1:
             return _available
 
-    # LM Studio / llama.cpp style: context window is reported in tokens but the
-    # prompt size is reported in CHARACTERS, e.g.
-    #   "maximum context length is 65536 tokens ... your prompt contains 77409
-    #    characters ...".
-    # Estimate the input tokens conservatively (~3 chars/token, which
-    # over-reserves the input so the retried output cap stays safely inside the
-    # window) and leave the remainder of the window for output.
-    _m_ctx_tok = re.search(r'maximum context length is (\d+)\s*token', error_lower)
-    _m_chars = re.search(r'prompt contains (\d+)\s*character', error_lower)
-    if _m_ctx_tok and _m_chars:
-        _ctx = int(_m_ctx_tok.group(1))
-        _est_input = (int(_m_chars.group(1)) + 2) // 3
-        _available = _ctx - _est_input
-        if _available >= 1:
-            return _available
-
     return None
 
 
@@ -1812,43 +1784,10 @@ def get_model_context_length(
         if ctx is not None:
             save_context_length(model, base_url, ctx)
             return ctx
-    # 5f. OpenRouter live /models metadata — authoritative for OpenRouter-routed
-    # models. OpenRouter's catalog carries per-model context_length (e.g.
-    # anthropic/claude-fable-5 -> 1M) and refreshes as new slugs ship, so it
-    # must win over both models.dev (step 5g) and the hardcoded family catch-all
-    # (step 8). Before this branch, an OpenRouter selection set
-    # effective_provider="openrouter", which (a) made the models.dev lookup miss
-    # brand-new slugs and (b) skipped the step-6 OR fallback (gated on `not
-    # effective_provider`), so a fresh slug like claude-fable-5 fell through to
-    # the generic "claude": 200K entry and under-reported a 1M window. Mirrors
-    # the dedicated Nous/Copilot/GMI branches above.
-    if effective_provider == "openrouter":
-        metadata = fetch_model_metadata()
-        entry = metadata.get(model)
-        if entry:
-            or_ctx = entry.get("context_length")
-            # Guard against the known OpenRouter Kimi-family 32k underreport
-            # (same class the hardcoded overrides exist to mitigate).
-            if isinstance(or_ctx, int) and or_ctx > 0 and not (
-                or_ctx == 32768 and _model_name_suggests_kimi(model)
-            ):
-                return or_ctx
-
     if effective_provider:
         from agent.models_dev import lookup_models_dev_context
         ctx = lookup_models_dev_context(effective_provider, model)
         if ctx:
-            # MiniMax M3: models.dev reports 512K but actual context is 1M.
-            # Prefer hardcoded catalog over stale probe value.
-            if _model_name_suggests_minimax_m3(model):
-                catalog = DEFAULT_CONTEXT_LENGTHS.get("minimax-m3")
-                if catalog and ctx < catalog:
-                    logger.info(
-                        "Rejecting models.dev context=%s for %r "
-                        "(MiniMax-M3 underreport); using hardcoded default %s",
-                        ctx, model, f"{catalog:,}",
-                    )
-                    ctx = catalog
             return ctx
 
     # 6. OpenRouter live API metadata — provider-unaware fallback.