fix: primeFold retries with demoted inline-think mirror (issue #64)

[ranxianglei]

Problem

Follow-up to #122 (issue #64, responses variant). Verified on a real glm-5.3 session: restart still showed Blocks: none until the first provider request.

Root cause (this variant): on glm/deepseek/qwen-style openai-completions profiles the host demotes unsigned thinking to text (transform-messages → renderDemotedThinking) and serializes it INLINE as a <think>…</think> tag inside the content string — there is no reasoning_content field. The primeFold mirror (viewToCoreStream) emitted reasoning pieces instead, splitting each thinking turn into reasoning+text while the live wire carried one text piece. The span fingerprints landed in different spaces, every in-stream compress replay was rejected (fold-replay-stale reason=fp), and the blocks only re-materialized at the first provider request.

Reconstruction rule verified byte-exact against a real wire dump (94/94 assistant messages match, dump req_7080.json, 208 msgs):

content = blocks in content order:
  thinking -> "<think>\n" + thinking + "\n</think>"  (+ "\n" if another block follows)
  text     -> stripRefTag(text)  (leading whitespace preserved; empty -> dropped)
no separator between blocks; no reasoning_content field

Fix

• viewToCoreStream: new opts.demoteThinking variant that rebuilds assistant content byte-exactly per the rule above (no reasoning_content); default path unchanged.
• runtime.ts primeFold: when the openai mirror yields zero blocks but the view contains compress calls, refold once with the demoted variant (preview makes the retry a fresh-slot full refold).

Tests

• wire-transform.test.ts: byte-exact unit test for the demoted serialization (multi-block glue, text-only, whitespace-only-drop, default variant unchanged).
• prime-provider-restart.test.ts: provider-mode restart regression with a glm-style wire (inline think tags, no reasoning_content) — block must be rebuilt before the first provider request. Verified the test guards the fix: disabling the retry fails exactly this test.

Full suite: 260 pass / 0 fail; tsc --noEmit clean.