Problem

iMessage (and likely other channel) responses have 1-2 blank lines prepended before the actual text content when using extended thinking mode.

Root Cause

Anthropic models in extended thinking mode emit a \n\n text content block before the thinking block. The streaming/block-flush path preserves these leading newlines because:

1. emitBlockChunk() in pi-embedded-subscribe.ts uses .trimEnd() instead of .trim() — preserves leading newlines
2. collapseConsecutiveDuplicateBlocks() in pi-embedded-helpers/errors.ts returns the original untrimmed text when there's only one paragraph block (early return if (blocks.length < 2) return text;)
3. sanitizeUserFacingText() doesn't trim the final output

The final payloads path (extractAssistantText()) is NOT affected because it trims individual content blocks and filters empties.

Fixes (defense in depth)

1. emitBlockChunk: .trimEnd() → .trim() — stops leading newlines at the source
2. collapseConsecutiveDuplicateBlocks: early return now returns trimmed instead of text — fixes the sanitizer
3. sanitizeUserFacingText: added .trim() to final return — safety net for all paths

Testing

• Verified compiled JS reflects all three changes
• No behavior change for well-formed text (already trimmed)
• Only affects text with leading whitespace, which should never be user-facing

Fixes #7689

Greptile Overview

Greptile Summary

This PR addresses leading blank lines in streaming/block-flush output (notably in iMessage) by trimming whitespace earlier and adding a defensive trim in the user-facing sanitizer.

Changes are localized to the embedded Pi streaming path (src/agents/pi-embedded-subscribe.ts) and the shared error/text sanitization helpers (src/agents/pi-embedded-helpers/errors.ts), so the fix should apply across any channels that consume those paths.

Confidence Score: 3/5

• This PR is close to safe to merge, but has one edge-case that can still preserve whitespace-only output in the sanitizer path.
• The core trimEnd→trim change in the streaming path is straightforward, but the helper collapseConsecutiveDuplicateBlocks() still returns the untrimmed original text for the all-whitespace case, which undermines the stated ‘defense in depth’ intent for leading-newline removal in some scenarios.
• src/agents/pi-embedded-helpers/errors.ts

Context used:

• Context from dashboard - CLAUDE.md (source)
• Context from dashboard - AGENTS.md (source)