fix(tool-schemas): reactive strip of pattern/format on llama.cpp grammar 400s

MCP servers commonly emit JSON Schema `pattern` (e.g. `\\d{4}-\\d{2}-\\d{2}`
for date-time params) and `format` keywords. llama.cpp's
`json-schema-to-grammar` converter rejects regex escape classes
(\\d/\\w/\\s) and most format values, returning HTTP 400
"parse: error parsing grammar: unknown escape at \\d" — the whole request
fails.

Cloud providers (OpenAI, Anthropic, OpenRouter, Gemini) accept these
keywords fine and use them as prompting hints. Stripping unconditionally
loses useful hints for every cloud user to fix a llama.cpp-only bug.

Approach: classify the llama.cpp grammar-parse 400 in the error
classifier, and on match do a one-shot in-place strip of pattern/format
from `self.tools`, then retry. Follows the existing
`thinking_signature` recovery pattern. Cloud users hit zero overhead;
llama.cpp users pay one failed request per session.

Changes
- agent/error_classifier.py: new `FailoverReason.llama_cpp_grammar_pattern`
  + narrow HTTP-400 branch matching "error parsing grammar",
  "json-schema-to-grammar", or "unable to generate parser ... template".
- tools/schema_sanitizer.py: new `strip_pattern_and_format()` helper —
  reactive, walks schema nodes, skips property names (search_files.pattern
  survives). Returns strip count for logging.
- run_agent.py: new one-shot recovery block in the retry loop. Strips,
  logs, continues. Falls through to normal retry if nothing to strip.
- tests: 4 classifier tests (3 variants + 1 non-400 negative), 7 strip
  tests including the property-name preservation and idempotency checks.

Co-authored-by: Chris Danis <cdanis@gmail.com>

agent/error_classifier.py

@@ -55,6 +55,7 @@ class FailoverReason(enum.Enum):
     thinking_signature = "thinking_signature"  # Anthropic thinking block sig invalid
     long_context_tier = "long_context_tier"    # Anthropic "extra usage" tier gate
     oauth_long_context_beta_forbidden = "oauth_long_context_beta_forbidden"  # Anthropic OAuth subscription rejects 1M context beta — disable beta and retry
+    llama_cpp_grammar_pattern = "llama_cpp_grammar_pattern"  # llama.cpp json-schema-to-grammar rejects regex escapes in `pattern` / `format` — strip from tools and retry
 
     # Catch-all
     unknown = "unknown"                  # Unclassifiable — retry with backoff
@@ -470,6 +471,31 @@ def classify_api_error(
             should_compress=False,
         )
 
+    # llama.cpp's ``json-schema-to-grammar`` converter (used by its OAI
+    # server to build GBNF tool-call parsers) rejects regex escape classes
+    # like ``\d``/``\w``/``\s`` and most ``format`` values. MCP servers
+    # routinely emit ``"pattern": "\\d{4}-\\d{2}-\\d{2}"`` for date/phone/
+    # email params. llama.cpp surfaces this as HTTP 400 with one of a few
+    # recognizable phrases; on match we strip ``pattern``/``format`` from
+    # ``self.tools`` in the retry loop and retry once. Cloud providers are
+    # unaffected — they accept these keywords and we never hit this branch.
+    if (
+        status_code == 400
+        and (
+            "error parsing grammar" in error_msg
+            or "json-schema-to-grammar" in error_msg
+            or (
+                "unable to generate parser" in error_msg
+                and "template" in error_msg
+            )
+        )
+    ):
+        return _result(
+            FailoverReason.llama_cpp_grammar_pattern,
+            retryable=True,
+            should_compress=False,
+        )
+
     # ── 2. HTTP status code classification ──────────────────────────
 
     if status_code is not None: