Make Codex workspace trust opt-in in compile-agent

[myobie]

Summary

• Make Codex workspace trust an explicit st2 compile-agent --harness codex --trust-workspace opt-in.
• Keep default generated output and the maintained Codex declaration free of project trust overrides.
• Serialize the declared workspace into argv-local Codex TOML with an exact decoded byte-for-byte key.
• Reject --trust-workspace for non-Codex harnesses before any catalog output is written.
• Keep Agent Spec, validation, reconciliation, runtime, and catalog behavior harness-agnostic.

Current-main integration

• Merged live main ea58cda7d5ffd8a64cf157259425c6bd26549cb4 normally.
• Exact corrected head: 70b447e3b7a67b979b9a59b472736d55b5124cea.
• The PR-local diff is exactly six files: the generator and CLI wiring, focused tests, and three authoring/example surfaces.
• No force push, runtime rollout, catalog mutation, deploy, or reconcile occurred.

Acceptance coverage

• Default Codex generation contains neither -c nor a projects trust override.
• Explicit Codex opt-in decodes through KDL and TOML to the exact workspace bytes.
• Claude plus --trust-workspace fails visibly before creating the catalog.
• Maintained hand-authored Codex examples remain trust-free by default.

Verification at 70b447e3b7a67b979b9a59b472736d55b5124cea

• cargo test --test compile_agent -- --test-threads=1: PASS (6/6)
• cargo test --all-targets --all-features -- --test-threads=1: PASS
• Scoped changed-path Clippy with warnings denied: PASS
• rustfmt --check src/compile_agent.rs: PASS
• git diff --check origin/main...HEAD: PASS
• Hosted Nix: PASS — run 30637552373 / job 91178891363

Repo-wide Clippy still stops on two pre-existing live-main lints in eval_run::wait_done and tests/eval_run_e2e.rs; neither file is changed by this PR.

The corrected exact head is held for CoS review before merge.

[myobie]

@schickling-assistant — review requested on exact head 7e52937eda0feb755564f6d50853fa7a551e0d32. You are authorized to merge on approval. If you request changes or reject it, please return it to me for correction. No catalog, host, or runtime rollout is part of this PR.

[myobie]

Correction complete at exact head 70b447e3b7a67b979b9a59b472736d55b5124cea. Default output is trust-free; explicit Codex opt-in, exact workspace-byte round-trip, and fail-before-write unsupported-harness behavior are covered. Local all-target/all-feature tests and hosted Nix run 30637552373 are green. Holding this PR open and unmerged for the required CoS review; no runtime or catalog rollout occurred.