feat: best-effort compact large tool schemas

[celia-oai]

Why

The dev/cc/ref-def branch preserves richer JSON Schema detail for connector tools, including $defs and nested shapes. That improves fidelity, but it pushes the largest connector schemas well past the intended tool-schema budget. This PR adds a best-effort compaction pass for unusually large tool input schemas so the p99 and max tails stay small while ordinary schemas are left alone.

What Changed

• Added best-effort large-schema compaction in codex-rs/tools/src/json_schema.rs after schema sanitization and definition pruning.
• Compaction runs as a waterfall only while the compact JSON budget proxy is exceeded:
  1. Strip schema description metadata.
  2. Drop root $defs / definitions.
  3. Collapse deep nested complex schema objects to {}.
• Kept top-level argument names and immediate schema shape where possible.

Corpus Results

Scope: 2,025 schemas under golden_schemas, all parsed successfully. Token count is o200k_base over compact JSON from parse_tool_input_schema.

Percentile	Before origin/main 4dbca61e20	After branch dev/cc/ref-def f9bf071758	After this PR
p0	9	9	9
p10	59	63	63
p25	81	86	86
p50	114	127	125
p75	174	205	202
p90	295	335	322
p95	391	526	422
p99	794	1,303	689
max	2,836	3,337	887

After this PR, 0 / 2,025 schemas are over 1k tokens.

Compaction Savings

These are cumulative waterfall stages over the same corpus. Later passes only run for schemas that are still over the compact JSON budget proxy.

Stage	Total tokens	Step savings	Schemas changed by step
No compaction	391,862	-	-
Strip schema description metadata	350,961	40,901	66
Drop root $defs / definitions	340,683	10,278	13
Collapse deep complex schemas to {}	335,875	4,808	6

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