pydantic--pydantic-ai/.github/workflows/shared/prompts/pydantic-ai-roundtrip-sweep.md

Pydantic AI Round-Trip Sweep

Objective

Find one concrete state-loss bug across a serialize → deserialize boundary — the highest-density reproducible cluster in this repo. Pick one boundary per run and audit it deeply:

• ModelMessagesTypeAdapter / to_jsonable_python ↔ ModelMessage round-trip.
• Agent message-history dump/load (new_messages, all_messages, message_history re-feeding).
• AG-UI adapter and Vercel AI adapter request/response conversion.
• Temporal / durable-exec serialization (value_to_type, activity payloads).
• Deferred-tool / tool-approval round-trip across a run boundary.

How to Verify — mandatory

Construct messages that include the edge-case parts most likely to be lost: thinking/reasoning parts, tool calls + tool returns (with ids), multimodal/binary content, retry/error parts, builtin-tool calls, usage and timestamps, custom result_type/output objects. Then round-trip them through the chosen boundary and assert structural equality (not just "no exception"). Write this as a new minimal test; do not run and report the existing suite. The bug must be one you triggered and observed.

What to Look For

• Fields silently dropped or defaulted (timestamps, ids, part kinds, usage).
• Type drift: str where a model/object is expected after reload; dict not re-validated into the proper part type.
• Ordering changes (tool call/return pairing broken after reload).
• Asymmetric adapters (encode then decode ≠ identity).
• Re-fed message_history changing run behavior vs the original run.

What to Skip

• Speculation without a failing reproduction.
• By-design lossy fields explicitly documented as such.
• Behavior already tracked by an open issue or fixed by an open PR — search both first.

Deduplication — mandatory BEFORE filing an issue

The gap may already be tracked by an open issue or already fixed by an open PR — check both. List them through the proxied gh CLI and filter locally — the /search/issues endpoint is blocked by the firewall proxy and there are no mcp__github__* tools.

(a) Existing issues — first check this sweep's own prior findings with a tight, server-side label filter (?labels= on the issue-list endpoint is allowed even though /search/issues is not):

gh api 'repos/pydantic/pydantic-ai/issues?state=open&labels=roundtrip-sweep&per_page=100' \
  --jq '.[] | select(.pull_request == null) | {number, title}'

Only if that is inconclusive, widen to a full open-issue scan and grep locally for "round-trip", "serialize", and the boundary/function you investigated:

gh api --paginate 'repos/pydantic/pydantic-ai/issues?state=open&per_page=100' \
  --jq '.[] | select(.pull_request == null) | {number, title, labels: [.labels[].name]}'

(b) Existing PRs — a fix may already be open (and even approved). List open PRs and scan for one touching the failing symbol or file:

gh api --paginate 'repos/pydantic/pydantic-ai/pulls?state=open&per_page=100' \
  --jq '.[] | {number, title}'

If a matching open issue or PR exists, call mcp__safeoutputs__noop immediately instead of filing. If a PR looks related but you cannot confirm it covers this exact gap, still file but fill in the optional Possibly addressed by #<N> row at the top of the body template (see Issue Format), linking that PR.

Sandbox notes

• Read files in large ranges (500+ lines per call). Do NOT read in 30–80 line chunks.
• Use the native Grep and Glob tools for codebase search.

Quality Gate — When to Noop

mcp__safeoutputs__noop is the expected outcome most runs. Call mcp__safeoutputs__noop unless you have a concrete, minimal, failing round-trip reproduction with observed output.

Issue Format

Title: <boundary>: <what is lost> on round-trip

Body: (include the first row only for an uncertain PR match; omit it otherwise)

Possibly addressed by # — [link the related open PR]

Impact

[Who is affected; e.g. resumed runs, Temporal workflows, AG-UI clients]

Boundary & Code Path

[Which serialize/deserialize path; file:line]

Reproduction

[The new round-trip test you wrote — full code — and the command]

Expected vs Actual

Expected: input == output. Actual: [diff of what changed]

Evidence

• [Captured output / diff; path:line references]

Adversarial review

• Reproduced on main: [exact command + real captured output]
• Existing tests checked: [adapter/serialization tests read; none assert this loss is intentional, and the fix doesn't break them]
• Ruled out by-design: [programmatic-only field / request-vs-response union placement / maintainer decision checked]
• Not a duplicate: [label-filtered dedup returned nothing]