V2: public context and model-aware runner history diverge across native checkpoints #425

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1. drexb-ops commented on Sep 17, 2026

   

   drexb-ops

   on Sep 17, 2026

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   Added an isolated adapter reproduction using official v2.0.3 toLLMMessages: public view [nativeCheckpoint, nextUser], outgoing view [originalUser, originalAssistant, nextUser] (the incompatible-provider re-expansion described by host history code). ACP reports a valid projection, but the checkpoint claims outgoing indexes [0,1] as opaque; neither original message ID is addressable. Normalizing that same public view without outgoing messages (the direct-tool path) gives the checkpoint zero parts. This confirms the adapter consequence. A full installed-host cross-provider regression remains required.

   🚀React with 🚀1Reacted by ranxianglei
2. ranxianglei commented on Sep 17, 2026

   

   ranxianglei

   on Sep 17, 2026

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   [bot] 🏷 Confirmed your reproduction against the fork source at b73c4cd (tip of 2026-09-17_opaque-compaction-restore). Root cause is pinpointed and the fix is scoped. Working on it now.

   Root Cause

   claimCheckpointRanges (lib/v2/projection/normalize.ts:480-506) assigns outgoing indices to a provider-checkpoint by positional inference: it takes every unclaimed outgoing message index between the previous source's last outgoing index and the next source's first outgoing index, and claims them all as the checkpoint's content.

   // normalize.ts:480-506 (simplified)
   const start = previous === undefined ? 0 : previous + 1
   const end = next === undefined ? messages.length : next
   for (let index = start; index < end; index++) {
       if (!claimed.has(index)) {
           claimed.add(index)
           checkpoint.outgoingMessageIndices.push(index)
       }
   }

   Your repro maps exactly onto this:

   View	Contents
   Public (ctx.session.context)	[nativeCheckpoint, nextUser]
   Outgoing (event.messages)	[originalUser, originalAssistant, nextUser]

   Walkthrough:

   1. nextUser correlates by ID → outgoing index 2.
   2. nativeCheckpoint is a provider-checkpoint (compaction + status:"completed" + providerContext), so it's skipped in the main ID-correlation loop (normalize.ts:658).
   3. claimCheckpointRanges runs: previous=undefined→start=0, next=2→end=2. Claims outgoing [0, 1] as the checkpoint's.
   4. Those two indices are the re-expanded originals, not checkpoint content. They're now marked opaque under the checkpoint's ownership. Neither original ID is addressable.
   5. Direct-tool path (outgoing=[]): start=0, end=0 → zero indices → buildProviderCheckpoint iterates nothing → zero parts.

   This is the "infer removability from array positions" anti-pattern the issue calls out. It happens to work in the compatible case (one unclaimed message in the range = the checkpoint itself) but silently misattributes in the incompatible case.

   Fix Plan

   Working on branch off fork/2026-09-17_opaque-compaction-restore:

   1. Remove positional inference for provider-checkpoints. A checkpoint only claims outgoing indices it can positively identify. Since checkpoints don't carry a stable outgoing ID (they're skipped in the ID-correlation loop), they get no outgoing indices from positional inference. Their normalized content is rendered from the source compaction data instead of from outgoing messages.

   2. Uncorrelated outgoing stays opaque. The re-expanded originals (or any other host-added content) remain uncorrelated → opaque → provider-owned. No mutation risk.

   3. Direct-tool path renders checkpoint from source. buildProviderCheckpoint falls back to the compaction's own text when it has no outgoing indices, eliminating the zero-parts gap.

   4. Tests (per acceptance criteria):

      • Compatible native checkpoint (same model): checkpoint correlates, content renders correctly
      • Incompatible model switch with re-expansion: checkpoint has no outgoing indices, originals stay opaque, no positional misattribution
      • Direct compress/decompress against both views (with and without outgoing)
      • Disclose unsupported windows: when public API can't represent the divergence, log + fail closed rather than guess

   5. No version bump, no publish, no merge. Fork PR referencing this issue.

   Proceeding with implementation. Will follow up here with the PR link once tests pass and dual review is done.
3. ranxianglei commented on Sep 17, 2026

   

   ranxianglei

   on Sep 17, 2026

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   继续
4. ranxianglei

   added a commit that references this issue on Sep 17, 2026

   fix: keep V2 patches alive when an uncorrelated provider checkpoint i…

   ...

   3765402
5. ranxianglei commented on Sep 17, 2026

   

   ranxianglei

   on Sep 17, 2026

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   Done — the fix is implemented, dual-reviewed, and submitted as drexb-ops#4 (V2 dev line, base master). Two commits:

   1. fix: stop inferring V2 provider-checkpoint ownership from array position (71458d18)

   • claimCheckpointRanges now collects the unclaimed candidates inside the positional window and claims a provider checkpoint only when exactly one candidate exists. >1 = re-expanded originals after an incompatible model switch → left uncorrelated, so every original stays individually addressable instead of being swallowed into one opaque blob. 0 = checkpoint absent from the outgoing view → also uncorrelated.
   • Uncorrelated checkpoints render from source data (lowerCompactionText) under an opaque origin key, fixing the zero-parts direct-tool gap. The rendered message carries a known normalized ID, so the patcher can never inject it into outgoing requests.
   • Unsupported windows are disclosed structurally: providerCheckpoint: true + empty outgoingMessageIndices, documented on V2ProvenanceEntry.providerCheckpoint.

   2. fix: keep V2 patches alive when an uncorrelated provider checkpoint is compressed away (37654026)

   • Found by the code reviewer during dual review — a real blocker my first draft introduced downstream: once the engine compresses the normalized checkpoint away, restoreMissingV2OpaqueSources rejected the entire patch ("no exact lowered correlation") and lib/v2/context.ts preserved the raw provider request — silently disabling every ACP edit for the rest of incompatible-switch sessions. Fix: skip (not reject) provider checkpoints with empty indices there; non-checkpoint opaque sources keep the fail-closed rejection. Regression test verified to fail against the unfixed code.

   Acceptance criteria coverage: compatible native checkpoint (regression lock, byte-identical behavior), incompatible model switch with re-expansion (originals addressable, host entries object-identical through the patch round-trip), direct view (checkpoint rendered from source data, never injected into requests), unsupported windows disclosed. No positional inference remains.

   Verification: 4 new tests, each bug-detection test empirically fails with its fix reverted (§5.7.3 methodology); v2 files 33/33; full suite 1414/1415 (single failure is tests/soft-block.test.ts hardcoding /tmp/opencode-dcp-dangerous-<pid> — environmental here, read-only /tmp, passes in CI, same as noted in PR #3); typecheck + build green; devlog complete. No version bump, no publish, no merge (merge stays human-side per repo rules).

   Two findings reported here per project rules (no new issues filed by me):

   1. Pre-existing, unrelated to this diff: the direct-tool view (normalizeV2ProjectedHistory(projected, [], …)) reports valid: false ("Patchable origin … has no exact lowered outgoing match") for any plain user/assistant source, even though .messages are fully built and consumed by lib/v2/host.ts:45,52. Verified identical at HEAD without this fix. Functional impact today is nil, but the invalid flag is misleading — worth its own issue if you want it tracked.
   2. Residual coverage gap: unit-level projection/patch/restore coverage now exists for both views, but there is no end-to-end decompress-through-both-views runtime test anywhere in the suite (V1 engine-level decompress tests don't traverse V2 projection/views). Tracked as a follow-up item here rather than scope-creeping this PR.

   Known residual limitations (all content-preserving, documented in devlog/…/DESIGN.md §5): a single re-expanded original is positionally indistinguishable from a decoded checkpoint (pre-existing behavior); an earlier incompatible checkpoint widens the next window (fail-safe); multi-message decoded checkpoints are now uncorrelated and rendered from source data.

   One topology note for transparency: this session's credentials lack push access to the drexb-ops fork, so the PR head branch lives in ranxianglei/opencode-acp (cross-fork PR — GitHub accepts it because your repo is the fork parent). If you'd prefer the branch moved into the fork, say the word.

   中文摘要：修复了 V2 公共上下文与模型感知历史在原生 checkpoint 处的分歧——不再按数组位置推断 checkpoint 归属（仅唯一候选才认领，重展开的原始消息保持可寻址），无关联时从源数据渲染并结构化披露不支持窗口；双 agent 评审发现并修复了一个会导致不兼容切换会话中 ACP 编辑被整体静默禁用的 restore 阻塞问题，PR 已提交待人工合并。
6. ranxianglei commented on Sep 17, 2026

   

   ranxianglei

   on Sep 17, 2026

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   [bot] 🏷 Status update (full report posted above): #425 is implemented, dual-reviewed, and submitted as drexb-ops#4 (base master, 2 commits, head 37654026).

   What was done

   1. claimCheckpointRanges no longer infers provider-checkpoint ownership from array position — claims only on exactly one unclaimed candidate; re-expanded originals after an incompatible model switch stay individually addressable, and checkpoints absent from the outgoing view are disclosed structurally (providerCheckpoint: true + empty indices) instead of being misclassified.
   2. Direct-tool view renders an uncorrelated checkpoint from source data (lowerCompactionText) instead of zero parts; the rendered message can never be injected into outgoing requests.
   3. Dual-agent review found one real blocker my first draft introduced downstream — restoreMissingV2OpaqueSources would reject the whole patch once such a checkpoint gets compressed away, silently disabling all ACP edits for those sessions. Fixed in commit 2 (lib/v2/projection/restore.ts skips uncorrelated provider checkpoints only; other opaque sources stay fail-closed) with a regression test verified to fail pre-fix.

   Verification: typecheck ✓, build ✓, v2 test files 33/33, full suite 1414/1415 (sole failure = environmental /tmp read-only in soft-block.test.ts, passes in CI); each bug-detection test empirically fails with its fix reverted; devlog complete. No version bump, no publish.

   Awaiting: human merge of the PR (merge is human-only per repo rules). Two follow-up findings for your triage (disclosed in the detailed report above): a pre-existing direct-view valid:false flag for plain user/assistant sources, and a missing end-to-end decompress-through-both-views test.

   中文摘要：#425 已完成并提交 PR（双评审通过、修复了评审发现的 restore 阻塞问题），等待人工合并。
7. ranxianglei

   added

   opencodev2

   on Sep 17, 2026
8. ranxianglei commented on Sep 19, 2026

   

   ranxianglei

   on Sep 19, 2026

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   opencodeV2 use https://github.com/ranxianglei/billion-context
9. ranxianglei

   closed this as completedon Sep 19, 2026