tui: check the model secret parse-only at startup

[nishu-builder]

Stack 1/2 (base for #170 — the sidebar-metadata cache).

Problem

Starting caos tui resolved the whole secret store before the first draw: build_secret_store ingests the workspace tree and eval-paths every reader= expression, and resolving DEEP-DEPS/llm-step dispatches real computation — the deepening run re-keyed by any tracked edit, plus rustc worker builds whenever llm-step's inputs (std/llm-*, their tool deps, rust/crates/conversation-protocol) changed. After such a build the tui sat on a blank terminal for the whole compile (~30s observed), answering a question startup never asked: it only needs to know whether an anthropic-api-key secret is configured.

Change

Split the store loader:

• caos: new load_local_secrets — the transport-free half of build_secret_store (specs parsed, values read, readers left as the declared expressions) — and local_secret_names on top of it. build_secret_store now consumes the shared loader, so the two can never disagree on what the store declares.
• caos-cli: model_secret_missing() and ensure_conversation_secret() are parse-only and no longer take a transport; require_model_secret generalizes over names. The first-run setup's post-install proof is parse-only too.
• A malformed spec or unreadable value file still fails readably at the shell prompt. Reader resolution moves entirely to the turn that sends a request — behind the tui's progress UI, where build_secret_store remains the loader (conversation_secret_store).
• TUI.md updated to describe the parse-only check.

Validation

• cargo check --workspace clean; cargo fmt --check clean; clippy shows only a pre-existing chunks_exact warning in untouched code.
• Full caos (32), caos-cli lib (51) and tui bin (138) suites green, including two new tests for the parse-only loader (reads specs/values without resolving readers; fails loudly on a missing value file).
• Not run here (no nix / no stack in this environment): nix build and the salted run-tool test gate — no new files or include_str!s are added, but worth a salted run before merge.

🤖 Generated with Claude Code

https://claude.ai/code/session_01AZgAh1BJk17ge3SasEaCJJ