[tsankotsanev]

Approved issue: #785

Harness coverage (required)

For each entry select: covered / not applicable — surface does not exist there / NOT covered.

• OpenCode 1: not applicable - surface does not exist there (the provider dispatch structure check lives only in packages/pi-plugin/src/pi-dispatch-structure.ts; no equivalent in packages/plugin)
• OpenCode 2: not applicable - surface does not exist there (same as OpenCode 1)
• Pi: covered (shared payloadStructure code path; Pi's providers do not emit these control rows, so its behavior is unchanged)
• OMP: covered (the fix targets the rows Oh My Pi's Anthropic provider appends)
• Rust module: not applicable - surface does not exist there (no dispatch structure check in crates/)

What and why

Oh My Pi's Anthropic provider (insertAnthropicControlMarkers in pi-ai/src/providers/anthropic.ts, 18.12.6) appends request-control system messages while it builds the request: tool_addition / tool_removal blocks when the session's recorded tool set differs from the current one, and empty effort-only controls (content: []). This happens after the context pass, so the prepared plan never contains them.

payloadStructure skipped system / developer messages only before the first conversation row, so a trailing control was counted as an extra row and every turn was refused with prepared turn structure ... expectedRole=missing actualRole=system comparison=count. Oh My Pi records the control only after a successful request, so an affected session could never recover on its own.

The fix skips system messages whose content is an array made only of tool_addition / tool_removal blocks (an empty array included). A system row carrying any other content (a string, a text block, or a control mixed with text) is still counted and compared, so unprepared system text keeps refusing.

Tests

New packages/pi-plugin/src/issue-785-request-controls.test.ts:

• An Anthropic payload ending in a tool_addition control, a mixed tool_addition + tool_removal control, or an empty effort-only control has no mismatch against the plan without it. Without the fix this fails with row=4 expectedRows=4 actualRows=5 expectedRole=missing actualRole=system ... comparison=count, the reported refusal.
• An unprepared system row with string content, a text block, or a control mixed with text still refuses, both trailing and mid-history.

Ran in packages/pi-plugin:

• bun test src/issue-785-request-controls.test.ts src/issue-686-midhistory-system.test.ts src/issue-686-system-head.test.ts src/pi-dispatch-structure-diagnostic.test.ts: 20 pass, 0 fail.
• bun run typecheck: clean.
• bunx biome check on both changed files: clean.
• bun run test: 3483 pass, 53 skip, 7 fail. The same 7 (index-env-guard, tag-snapshot-hydration-pi, context-handler-lkg-debug-assertions, lkg-fence-restart-regression x3, held-head-replay-witness) also fail on unmodified master in this environment.

The live behavior was also checked by applying the same change to the published 0.49.23 dist: the previously refused session replies normally and new sessions are unaffected.

[github-actions]

#785 has the design-approved label; this PR can be reviewed.