docs: D42 — streaming singleflight design ADR + v1.x safeguards (issue #16)

ADR 0005 Amendment 6 (D34) deferred streaming-path D4 singleflight to
v1.x with the note "the design alone warrants a dedicated ADR." Round-6
cold-audit F13 (issue #16) raised the sibling TOCTOU window between
server.mjs's preCheckHit peek and the streaming-branch spawn. D42
fulfils Amendment 6's deferral note by ratifying the v1.x design as
ADR 0005 Amendment 8 — design only, no implementation.

**Design ratified (ADR 0005 Amendment 8, 14 sections):**

1. New `cacheStore.getOrComputeStreaming(keyId, cacheKey, sourceFactory)`
   API with `{ stream, isFirst }` return shape. Mirrors the buffered
   path's `getOrCompute` to keep the cache API surface coherent.
2. `StreamingInflightEntry` shape — source iterator + AbortController +
   accumulated-chunks replay buffer + attached-clients Set + state
   flags + D38 spawn-slot tracker.
3. `AttachedClient` shape — per-client tee buffer + byte-size meter +
   late-joiner replay flag + done/resolveNext/rejectNext for the
   single-reader-multi-writer tee.
4. Tee fan-out loop (one reader drains source, fans chunks to all
   attached clients).
5. Late-joiner replay policy — accumulated chunks burst-drained on
   attach.
6. Cache TTL race during inflight — late joiners see the inflight entry
   and join; expired cache slot is overwritten by inflight completion.
7. D38 maxConcurrent coordination — only first caller acquires; release
   fires once on source-complete/error/abort.
8. New `STREAM_BACKPRESSURE` error code. NOT a hard trigger. Affected
   client gets synthetic `{ type: 'stop', finish_reason: 'length' }` +
   `[DONE]` (matches D35 #10 truncation marker).
9. Mid-stream disconnect — remove from attached set; if 0 remaining,
   abort source via AbortController.
10. Replay buffer cap (10 MB, matches D23 cache-entry cap) — over cap
    marks entry not cacheable, late joiners get backpressure error.
11. Observability — 4 new log events
    (streaming_inflight_join / source_done / abort,
    stream_backpressure_disconnect) + new
    `X-OLP-Streaming-Inflight: source | attached | solo` header.
12. Server.mjs wiring — replaces the current peek+spawn pattern;
    TOCTOU window closes because Map check+insert is synchronous.
13. Test surface (when implementation lands) — 10 scenarios covering
    single-client / 2-concurrent / 3-concurrent / mid-stream join /
    first-disconnect / all-disconnect / source-error / backpressure /
    D38 coordination / TTL race / replay cap / X-OLP-* header values.
14. Defaults — PER_CLIENT_QUEUE_CAP=1MB, ACCUMULATED_REPLAY_CAP=10MB,
    STREAM_BACKPRESSURE not in HARD_TRIGGER_CODES.

**Multi-layer safeguards (the maintainer asked: "保证后面这一块会被处理而不会被忽略"):**

1. **`docs/v1x-roadmap.md` (NEW)** — single living landing page for
   every Phase-1 deferral. 7 items at D42:
   - #1 Streaming SF (this amendment)
   - #2 Multi-key auth (lib/keys.mjs)
   - #3 Soft trigger reactivation (ADR 0004 Amendment 2)
   - #4 /health activeSpawns integration (D38)
   - #5 Provider-level cacheKeyFields mask (ADR 0005 Amendment 7)
   - #6 Streaming-path SPAWN_FAILED salvage
   - #7 AUTH_MISSING tuple test coverage (D40 follow-up)
   Each entry names the ratifying ADR, load-bearing code anchor
   (file:line), GitHub issue (if any), concrete start trigger, and
   estimated effort. Maintainer's session-startup discipline grep
   this file at sprint kickoff.

2. **Issue #16 STAYS OPEN** — not closed in D42. Body updated post-
   commit to reference Amendment 8 with status "design ratified;
   implementation pending." Do not close until §13 test surface is
   green on actual implementation.

3. **`lib/cache/store.mjs#getOrCompute` JSDoc** — TODO comment for the
   sibling streaming API pointing at Amendment 8 + v1x-roadmap.md #1.

4. **`server.mjs` streaming-branch entry (~line 810)** — TODO comment
   block citing Amendment 8 + issue #16 + roadmap.md #1, naming the
   exact code lines the v1.x impl will replace.

5. **`README.md § Known limitations` section** — new subsection
   surfaces 4 limitations to users (streaming SF / soft triggers /
   multi-key auth / cacheKeyFields mask), each linking to the
   v1x-roadmap.md entry.

6. **Amendment 8 § "Cross-references and safeguards"** — explicit
   cross-link block enumerating the above 4 anchors so a future
   ADR-only reader knows every breadcrumb.

**Maintainer decision recorded:** Option 1 (design ADR only) chosen
over Option 2 (design + implementation now). Rationale: 200-400 lines
of concurrency primitives + 15-20 tests is not "pre-Phase-2 cleanup"
in shape — it is real v1.x feature work. Shipping streaming SF in a
v0.1.1 patch release would muddy the Phase 1 / Phase 2 contract that
v0.1.0 ratified. Personal/family-scale load makes the deferral safe
at v0.1.

Changes (6 files, +165 / -0):

- `docs/adr/0005-cache-cross-provider.md` — Amendment 8 prepended
  (133 lines).
- `docs/v1x-roadmap.md` — NEW file (148 lines).
- `lib/cache/store.mjs` — getOrCompute JSDoc gains TODO block (8 lines).
- `server.mjs` — streaming-branch entry gains TODO block (6 lines).
- `README.md` — Known limitations section (9 lines).
- `CHANGELOG.md` — D42 sub-entry under Unreleased (9 lines).

No code-behavior change. No new tests. No package.json bump
(phase_rolling_mode).

Authority:
- ADR 0005 Amendment 8 (this commit) — design ratification
- ADR 0005 Amendment 6 (D34) — original deferral with "design ADR
  needed" note that this commit fulfils
- GitHub issue #16 (round-6 F13) — sibling TOCTOU; STAYS OPEN
- ADR 0002 Amendment 6 (D38) — tryAcquireSpawn semantics
- ADR 0004 Amendment 5 (D40) — observability pattern extension
- CC 开发铁律 v1.6 § 10.x — design-only amendment; fresh-context
  reviewer not required per Iron Rule 10 implementation-phase scope
- CLAUDE.md release_kit_overlay phase_rolling_mode — under Unreleased

Co-Authored-By: Claude Opus 4.7 <noreply@anthropic.com>

README.md

@@ -190,6 +190,15 @@ Phase 1 is in progress. This table reflects what is currently shipped vs. what i
 | `scripts/migrate-from-ocp.mjs` | 📋 Planned (Phase 7) | OCP → OLP migration tool |
 | `setup.mjs` | 📋 Planned | Setup wizard / initial config |
 
+### Known limitations
+
+Behaviors that work correctly at personal/family scale but have ratified follow-ups for a v1.x sprint. Single landing page: [`docs/v1x-roadmap.md`](./docs/v1x-roadmap.md).
+
+- **Streaming-path singleflight not implemented.** The cache layer's D4 singleflight (one spawn per identical concurrent request) is fully wired on the buffered path but NOT on the streaming path. N concurrent identical streaming requests at v0.1 will each spawn their own CLI process. Design ratified in [ADR 0005 Amendment 8](./docs/adr/0005-cache-cross-provider.md); implementation tracked via [issue #16](https://github.com/dtzp555-max/olp/issues/16) and [v1.x roadmap #1](./docs/v1x-roadmap.md). At family scale this is observably fine — every caller still receives the correct response; the cost is N CLI processes instead of one.
+- **Soft triggers configured but inert.** `routing.soft_triggers` in `~/.olp/config.json` is honored by the engine's evaluation logic but `quotaStatus()` polling is not wired (ADR 0004 Amendment 2). A startup warning fires if the field is non-empty so the inert state is visible.
+- **Multi-key auth not yet implemented.** All requests today share the cache namespace `__anonymous__`. The cache data model is keyed by `keyId` and ready to accept real identities when `lib/keys.mjs` lands. Tracked in [v1.x roadmap #2](./docs/v1x-roadmap.md).
+- **Provider-level `cacheKeyFields` mask not implemented.** Cache keys include every IR field including ones individual plugins drop at spawn (e.g., Anthropic plugin drops `temperature`). Spurious cache misses possible (extra spawn cost; never spurious hits). Conservative posture documented in [ADR 0005 Amendment 7](./docs/adr/0005-cache-cross-provider.md). Tracked in [v1.x roadmap #5](./docs/v1x-roadmap.md).
+
 ---
 
 ## Architecture