---
summary: "Reference: provider-specific transcript sanitization and repair rules"
read_when:
  - You are debugging provider request rejections tied to transcript shape
  - You are changing transcript sanitization or tool-call repair logic
  - You are investigating tool-call id mismatches across providers
title: "Transcript hygiene"
---

OpenClaw applies **provider-specific fixes** to transcripts before a run
(building model context). Most of these are **in-memory** adjustments used to
satisfy strict provider requirements. A separate session-file repair pass may
also rewrite stored JSONL before the session is loaded, but only for
malformed lines or persisted turns that are invalid durable records.
Delivered assistant replies are preserved on disk; provider-specific
assistant-prefill stripping happens only while constructing outbound
payloads.

When a repair occurs, the original file is written to a transient
`*.bak-<pid>-<ts>` sibling before the atomic replace, then removed once the
replace succeeds. The backup is retained only if cleanup itself fails, in
which case the path is reported back.

Scope includes:

- Runtime-only prompt context staying out of user-visible transcript turns
- Tool call id sanitization
- Tool call input validation
- Tool result pairing repair
- Turn validation / ordering
- Thought signature cleanup
- Thinking signature cleanup
- Image payload sanitization
- Blank text-block cleanup before provider replay
- Incomplete reasoning-only length-turn cleanup before provider replay
- User-input provenance tagging (for inter-session routed prompts)
- Empty assistant error-turn repair for Bedrock Converse replay

If you need transcript storage details, see
[Session management deep dive](/reference/session-management-compaction).

---

## Global rule: runtime context is not user transcript

Runtime/system context can be added to the model prompt for a turn, but it is
not end-user-authored content. OpenClaw keeps a separate transcript-facing
prompt body for Gateway replies, queued followups, ACP, CLI, and embedded
OpenClaw runs. Stored visible user turns use that transcript body instead of
the runtime-enriched prompt.

For legacy sessions that already persisted runtime wrappers, Gateway history
surfaces apply a display projection before returning messages to WebChat,
TUI, REST, or SSE clients.

---

## Where this runs

All transcript hygiene is centralized in the embedded runner:

- Policy selection: `src/agents/transcript-policy.ts`
  (`resolveTranscriptPolicy`, keyed on `provider`, `modelApi`, and `modelId`)
- Sanitization/repair application: `sanitizeSessionHistory` in
  `src/agents/embedded-agent-runner/replay-history.ts`

Separate from transcript hygiene, session files are repaired (if needed)
before load:

- `repairSessionFileIfNeeded` in `src/agents/session-file-repair.ts`
- Called from `src/agents/embedded-agent-runner/run/attempt.ts` and
  `src/agents/embedded-agent-runner/compact.ts`

---

## Global rule: image sanitization

Image payloads are always sanitized to prevent provider-side rejection due to
size limits (downscale/recompress oversized base64 images). This also helps
control image-driven token pressure for vision-capable models: lower max
dimensions reduce token usage, higher dimensions preserve detail.

Implementation:

- `sanitizeSessionMessagesImages` in
  `src/agents/embedded-agent-helpers/images.ts`
- `sanitizeContentBlocksImages` in `src/agents/tool-images.ts`
- Max image side is configurable via `agents.defaults.imageMaxDimensionPx`
  (default: `1200`)
- Blank text blocks are removed while this pass walks replay content.
  Assistant turns that become empty are dropped from the replay copy; user
  and tool-result turns that become empty receive a non-empty
  omitted-content placeholder.

---

## Global rule: malformed tool calls

Assistant tool-call blocks missing both `input` and `arguments` are dropped
before model context is built. This prevents provider rejections from
partially persisted tool calls (for example, after a rate limit failure).

Implementation:

- `sanitizeToolCallInputs` in `src/agents/session-transcript-repair.ts`
- Applied in `sanitizeSessionHistory`
  (`src/agents/embedded-agent-runner/replay-history.ts`)

---

## Global rule: incomplete reasoning-only turns

Assistant turns that hit the provider output limit with only thinking or
redacted-thinking content are omitted from the in-memory replay copy. Such
turns contain incomplete provider state and may carry a partial thinking
signature.

Empty length turns remain unchanged, as do length turns with visible text,
tool calls, or unknown content blocks. Stored transcripts are not rewritten.

Implementation: `normalizeAssistantReplayContent` in
`src/agents/embedded-agent-runner/replay-history.ts`

---

## Global rule: inter-session input provenance

When an agent sends a prompt into another session via `sessions_send`
(including agent-to-agent reply/announce steps), OpenClaw persists the
created user turn with `message.provenance.kind = "inter_session"`.

OpenClaw also prepends a same-turn `[Inter-session message] ... isUser=false`
marker before the routed prompt text so the active model call can
distinguish foreign session output from external end-user instructions. This
marker includes the source session, channel, and tool when available. The
transcript still uses `role: "user"` for provider compatibility, but the
visible text and provenance metadata both mark the turn as inter-session
data.

During context rebuild, OpenClaw applies the same marker to older persisted
inter-session user turns that only have provenance metadata.

---

## Provider matrix (current behavior)

**OpenAI / OpenAI Codex**

- Image sanitization only.
- Drop orphaned reasoning signatures (standalone reasoning items without a
  following content block) for OpenAI Responses/Codex transcripts, and drop
  replayable OpenAI reasoning after a model route switch.
- Preserve replayable OpenAI Responses reasoning item payloads, including
  encrypted empty-summary items, so manual/WebSocket replay keeps required
  `rs_*` state paired with assistant output items.
- Native ChatGPT Codex Responses follows Codex wire parity by replaying
  prior Responses reasoning/message/function payloads without prior item
  IDs while preserving session `prompt_cache_key`.
- OpenAI Responses-family replay preserves canonical `call_*|fc_*`
  same-model reasoning pairs, but deterministically normalizes malformed or
  overlong `call_id`/function-call item ids before pi-ai payload conversion.
- Tool result pairing repair may move real matched outputs and synthesize
  Codex-style `aborted` outputs for missing tool calls.
- No turn validation or reordering; no thought signature stripping.

**OpenAI-compatible Chat Completions**

- Historical assistant thinking/reasoning blocks are stripped before replay
  so local and proxy-style OpenAI-compatible servers do not receive
  prior-turn reasoning fields such as `reasoning` or `reasoning_content`.
- Current same-turn tool-call continuations keep the assistant reasoning
  block attached to the tool call until the tool result has been replayed.
- Custom/self-hosted model entries with `reasoning: true` preserve replayed
  reasoning metadata.
- Provider-owned exceptions can opt out when their wire protocol requires
  replayed reasoning metadata.

**Google (Generative AI / Gemini CLI / Antigravity)**

- Tool call id sanitization: strict alphanumeric.
- Tool result pairing repair and synthetic tool results.
- Turn validation (Gemini-style turn alternation).
- Google turn ordering fixup (prepend a tiny user bootstrap if history
  starts with assistant).
- Antigravity Claude: normalize thinking signatures; drop unsigned thinking
  blocks.

**Anthropic / Minimax (Anthropic-compatible)**

- Tool result pairing repair and synthetic tool results.
- Turn validation (merge consecutive user turns to satisfy strict
  alternation).
- Trailing assistant prefill turns are stripped from outgoing Anthropic
  Messages payloads when thinking is enabled, including Cloudflare AI
  Gateway routes.
- Pre-compaction assistant thinking signatures are stripped before provider
  replay when a session has been compacted. Thinking signatures are
  cryptographically bound to the conversation prefix at generation time;
  after compaction the prefix changes (summarized content replaces the
  original), so replaying the original signatures causes Anthropic to
  reject the request with "Invalid signature in thinking block". The
  thinking text is preserved as an unsigned block and then handled by the
  rule below.
- Thinking blocks with missing, empty, or blank replay signatures are
  stripped before provider conversion. If that empties an assistant turn,
  OpenClaw keeps turn shape with non-empty omitted-reasoning text.
- Older thinking-only assistant turns that must be stripped are replaced
  with non-empty omitted-reasoning text so provider adapters do not drop
  the replay turn.

**Amazon Bedrock (Converse API)**

- Empty assistant stream-error turns are repaired to a non-empty fallback
  text block before replay. Bedrock Converse rejects assistant messages
  with `content: []`, so persisted assistant turns with `stopReason:
"error"` and empty content are also repaired on disk before load.
- Assistant stream-error turns with only blank text blocks are dropped from
  the in-memory replay copy instead of replaying an invalid blank block.
- Pre-compaction assistant thinking signatures are stripped before Converse
  replay when a session has been compacted, for the same reason as
  Anthropic above.
- Claude thinking blocks with missing, empty, or blank replay signatures
  are stripped before Converse replay. If that empties an assistant turn,
  OpenClaw keeps turn shape with non-empty omitted-reasoning text.
- Older thinking-only assistant turns that must be stripped are replaced
  with non-empty omitted-reasoning text so the Converse replay keeps
  strict turn shape.
- Replay filters OpenClaw delivery-mirror and gateway-injected assistant
  turns.
- Image sanitization applies through the global rule.

**Mistral (including model-id based detection)**

- Tool call id sanitization: strict9 (alphanumeric, length 9).

**OpenRouter Gemini**

- Thought signature cleanup: strip non-base64 `thought_signature` values
  (keep base64).

**OpenRouter Anthropic**

- Trailing assistant prefill turns are stripped from verified OpenRouter
  OpenAI-compatible Anthropic model payloads when reasoning is enabled,
  matching direct Anthropic and Cloudflare Anthropic replay behavior.

**Everything else**

- Image sanitization only.

---

## Historical behavior (pre-2026.1.22)

Before the 2026.1.22 release, OpenClaw applied multiple layers of transcript
hygiene:

- A **transcript-sanitize extension** ran on every context build and could:
  - Repair tool use/result pairing.
  - Sanitize tool call ids (including a non-strict mode that preserved
    `_`/`-`).
- The runner also performed provider-specific sanitization, which
  duplicated work.
- Additional mutations occurred outside the provider policy, including
  stripping `<final>` tags from assistant text before persistence, dropping
  empty assistant error turns, and trimming assistant content after tool
  calls.

This complexity caused cross-provider regressions (notably
`openai-responses` `call_id|fc_id` pairing). The 2026.1.22 cleanup removed
the extension, centralized logic in the runner, and made OpenAI **no-touch**
beyond image sanitization.

## Related

- [Session management](/concepts/session)
- [Session pruning](/concepts/session-pruning)
