[BUG] Tool calls intermittently emitted as literal text (stray "count" + raw <invoke>) instead of executing — Opus 4.8, long Edit-heavy session

Summary

In long sessions on Claude Opus 4.8 (Claude Code CLI), the agent intermittently emits tool calls as literal text in the transcript instead of as executable tool_use blocks. The leaked text is prefixed with a stray count token followed by raw <invoke>…</invoke> XML. The call does not execute, the turn frequently ends immediately, and the malformed markup is shown to the user as the assistant message. Re-issuing the same call verbatim succeeds.

This appears to be the same class of bug as #64108 (which reports a stray court token — court ≈ count), and likely related to #64690, #64418, #64190, #65130, #64561, #64035, #63870, #61122, #63580. Filing a fresh report with a concrete, sustained long-session reproduction.

Symptom (exact)

Instead of an executed tool call, the visible assistant message contains:

count
<invoke name="Edit">
<parameter name="file_path">/path/to/file</parameter>
<parameter name="old_string">...</parameter>
<parameter name="new_string">...</parameter>
</invoke>

Also observed with <invoke name="Bash"> and <invoke name="Write">. Two tells:

• A leading stray count word.
• The <invoke> / <parameter> tags are not namespaced (i.e. plain <invoke> rather than the correct internal serialization).

Environment

• Claude Code CLI 2.1.161
• Model: Claude Opus 4.8
• OS: macOS
• Session: very long / high tool-composition — dozens of Edit/Write/Bash calls, 20+ files created across a multi-hour build.

When it happens (pattern)

• Strongly correlated with long / high-composition sessions — frequency rises as the session grows.
• Affects Edit and Write most, occasionally Bash/Read.
• Intermittent: the same call almost always succeeds when re-issued verbatim immediately afterward.
• When it occurs, the tool does not run and the turn ends ("just exits") with the raw markup as the message body. The user sees a confusing code-dump and nothing happens.
• In my session it recurred ~10+ times over the build.

Reproduction (conditions; not deterministic)

1. Start a long Opus 4.8 session in Claude Code CLI.
2. Do sustained Edit/Write-heavy work (e.g. scaffolding a project file-by-file with many small Edits/Writes).
3. As the session grows, tool calls intermittently serialize as plain count <invoke>… text instead of executing.

Not reliably reproducible on a single command, but reliably occurs given a long enough Edit/Write-heavy Opus 4.8 session.

Impact

• Heavy transcript noise; reads like a malfunction / random code dump to the user.
• Wasted turns — every occurrence must be detected and the call re-issued.
• Breaks flow in agentic/automated work and erodes user trust.

Hypothesis

The consistent count/court-prefixed, non-namespaced <invoke> corruption points at function-call serialization / tokenization corruption on the model/CLI side rather than a tool-side error — the tools execute fine when the markup is well-formed. Possibly the same root cause as #64418 ("serialized as plain text in high-composition sessions") and #64190 ("after /compact … whole tool calls emitted as <invoke> text").

Observed mitigations (not fixes)

• Re-issuing the call verbatim usually works.
• Starting a fresh / shorter session greatly reduces the frequency.