fix(agent): recover Qwen/Hermes wrapper calls, reject non-string payloads, unfilter codex models

[Spoofiecus]

Summary

Fixes three confirmed bugs in the Qwen/Hermes text-mode tool-call intake:

• Malformed Hermes/Qwen wrappers suppress later valid bare tool calls #6014: a malformed wrapper suppressed later valid bare tool calls. The bare-invoke fallback now masks consumed wrapper spans, so markup inside a malformed JSON payload still stays data while real calls after/between wrappers are recovered.
• Hermes/Qwen wrapper parsing treats closing markers inside JSON strings as delimiters #6013: a closer token inside a JSON string value ended the wrapper span early, so the body failed to decode. The parser retries with each later closer until the body decodes.
• Hermes/Qwen JSON tool calls accept non-string shell and Python payloads #6012: non-string command/code payloads were coerced into ToolBlock content that is not a str (crash/mangled execution). Now fail closed, matching the email-tools precedent.

Target branch

• This PR targets dev, not main.

Type of Change

• Bug fix (non-breaking - fixes a confirmed issue)

Linked Issue

Fixes #6014
Fixes #6013
Fixes #6012

Checklist

• I searched open issues and open PRs - this is not a duplicate.
• This PR targets dev
• My changes are limited to the scope described above - no unrelated refactors or whitespace changes mixed in.
• I actually ran the app (uvicorn app:app, native venv, 127.0.0.1:7001) and verified the change works. Details in How to Test.

How to Test

1. python -m pytest -q tests/test_tool_parsing_wrapper_recovery.py -> 7 passed (one per issue plus the agent: tool-call parsing and schema hardening subtracker #5333 and no-regression cases).
2. python -m pytest -q tests/test_tool_parsing_hermes_json.py tests/test_redos_xml_tool_parsers.py -> existing parser contracts still green (ReDoS bounds included).
3. Runtime: booted uvicorn app:app on 127.0.0.1:7001 with these changes; /api/health healthy.

Note: the #6218 codex-discovery fix was removed from this PR - #6244 already owns it.

[Spoofiecus]

Heads-up while comparing open PRs: this PR originally also carried the #6218 codex-discovery fix. #6244 by @ashvinctrl already owns that fix, so it has been removed here (diff now: the #6012/#6013/#6014 Qwen/Hermes parser fixes only). Deferring #6218 to #6244.