Bug: empty tool-call id/name wipe in llm-deepseek makes session history unloadable

[xiaofa-fenye]

Summary

DeepSeek official API SSE streams repeat id: "" / name: null on later tool_calls deltas of the same index (argument-only fragments). llm-deepseek's translate layer unconditionally overwrites the valid id/name captured from the first delta, so the assembled tool-call block ends up with empty id/name.

The empty-name call is then dispatched as unknown tool "", and the tool/result is persisted with an empty callId. On reload the session validator requires a non-empty callId for tool/result, so the whole session history fails to load:

SessionPersistenceCorruptionError: session event at seq 1077 message must have tool source

Reproduced on deepseek-v4-flash via provider deepseek-official.

Fix (available on fork)

Since external PRs are not accepted at the moment, the fix is committed to a fork:

• fork: https://github.com/xiaofa-fenye/deepseek-harness
• commit: xiaofa-fenye@9a3250e9e9

Changes:

• packages/llm/llm-deepseek/src/translate.ts — adopt only non-empty id/name; degenerate follow-up deltas no longer wipe valid values
• packages/llm/llm/src/assembler.ts — same sticky-id guard (defense for any adapter)
• packages/core/agent-loop/src/tool-calls.ts — synthesize call-synthetic-N for empty-id blocks so tool/call and tool/result stay correlated and sessions stay reloadable

Regression tests added in translate.spec.ts / assembler.spec.ts / loop.spec.ts — 101 tests pass.

Happy to rebase or adjust anything if the team wants to cherry-pick.

[weijiafu14]

Your diagnosis of the translate-layer overwrite matches what we measured from the outside — adding two datapoints that may help scope the fix:

The other accumulator in this ecosystem is structurally immune to exactly this input. We fault-injected the real pi-ai openai-completions accumulator (client/SSE parser/assembly unmodified, only wire bytes synthetic) with the exact shapes you describe — later deltas of the same index carrying id: "" / name: null, argument-only fragments — plus parallel calls with no ids at all: all assemble correctly, because blocks are keyed by index first and the first non-empty id/name wins, so an empty continuation cannot wipe anything. Per-case verdicts: accumulator-experiment.mjs / results (re-verified on latest 0.84.4). That first-non-empty-wins rule is a ready-made semantic for the llm-deepseek patch.

Live confirmation the id-carrying path works end to end on real api.deepseek.com via the pi-ai route: a multi-tool-call turn with distinct non-empty call ids and a fully parseable/reloadable history (provider-threads-e2e.json, case parallel-calls).

Related report with the same root shape, for cross-linking: #3090. Scope honesty: neither datapoint fixes llm-deepseek — they establish that the upstream wire shape is survivable and what the survival rule looks like.