feat(sync): absorb 54 curated upstream commits (session/provider/llm fixes + features)

[LeXwDeX]

Why

Phased upstream sync from sst/opencode (merge-base 7c0e1b43, 1176 upstream commits triaged). Per the delivery brief: cherry-pick only what is useful, never touch fork-owned designs, gate every batch.

What changed

• Session retry hardening (8): retry matching simplified + expanded (xAI capacity, network error variants, raw network_error finish), jitter-capped backoff, parent session header, session import errors, unknown config fields tolerated.
• Provider correctness (17): sonnet 5 / Grok / Meta / MiniMax / DeepSeek / Gemini / Qwen / OpenRouter sampling + reasoning fixes, Mistral tool-call ID normalization, SDK-keyed prompt cache selection, Bedrock unreplayable-reasoning cache filter, Azure gpt-5.5+ reasoningEffort, Copilot PDF detection, /connect authed providers.
• Core stability (10): external read path authorization, home-relative permission paths, git-only watcher, FFF cache cleanup, FSUtil.ensureDir AlreadyExists, MCP skill env field, unicode grep previews, oversized WebSocket fallback, remote skills refresh, models.dev modes as models.
• Features (7 + tests): MCP timeout split, LLM response reducers + reducer-law tests, request precedence, tool schema projections, model defaults/compatibility schema (#34436 prerequisite), strict tool passthrough, TUI subagent menu up-arrow exit.
• Server / ACP / TUI (5): 5xx proxy body logging, remote-workspace host-dir leak fix, ACP permission prompt enrichment, tmux ssh clipboard, skills doc path.
• Release material: .github/releases/v1.0.36.md series notes (both dev + stable channels render-verified).

Evidence

• Triage: 1160 upstream commits -> 799 clean vs fork-modified set; 359 touching fork code excluded; ~106 core-runtime candidates reviewed, 54 landed, 13 deliberately skipped (dependency drift / fork-owned designs).
• Gates at HEAD: bun typecheck (opencode/core/llm) PASS, test:dag-core 767 PASS, packages/llm 309/0 PASS, 505 targeted tests 0 fail.
• Two-axis review (Standards/Spec): 0 violations, 0 leaks, 0 scope creep; protected surfaces (DAG/SpecGit/release pipeline/TUI plugins) byte-identical where expected.

Checklist

• No fork-owned file touched (dag/, spec_git/, .github/releases additions only, release-fork.yml, feature-plugins/**)
• Skipped upstream commits verified absent (#45845, #36624 chain, #42160/#42164, #37562, #35636, #45784/#45849, #40718, #34081/#34082, #35175)
• typecheck + unit + dag-core gates green locally
• Release notes series file present and render-validated for both channels