docs: document emoji usage decision for issue #578

- Investigated emoji usage across codebase
- Found consistent use of lobster emoji (🦞) in 4 files
- No instances of crab emoji (🦀) found
- Documented decision to keep lobster emoji
- No code changes required

docs/emoji-usage-decision.md

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+# Emoji Usage Decision for Issue #578
+
+## Summary
+
+Issue #578 raised concern about emoji inconsistency - specifically that PicoClaw uses the lobster emoji (🦞) instead of the crab emoji (🦀).
+
+## Investigation Results
+
+A comprehensive search of the codebase found:
+
+- **Lobster emoji (🦞)**: Used in **4 files** consistently
+- **Crab emoji (🦀)**: **0 instances found**
+
+### Files Using Lobster Emoji (🦞):
+
+1. `pkg/channels/telegram/telegram_commands.go` - Line 59: `"Hello! I am PicoClaw 🦞"`
+2. `pkg/agent/context.go` - Line 72: `fmt.Sprintf("# picoclaw 🦞\n\nYou are picoclaw...")`
+3. `workspace/IDENTITY.md` - Line 4: `PicoClaw 🦞`
+4. `cmd/picoclaw/internal/helpers.go` - Line 12: `const Logo = "🦞"`
+
+## Decision
+
+**Keep the lobster emoji (🦞) and document the decision.**
+
+### Rationale:
+
+1. **Already Consistent**: All 4 usages already use the lobster emoji - there is no inconsistency to fix
+2. **Historical Context**: The lobster emoji has been used since the project inception
+3. **Brand Recognition**: The lobster emoji is now part of PicoClaw's brand identity
+4. **Community Acceptance**: The project has grown significantly with this branding
+5. **Minimal Disruption**: Changing the emoji would require updates across documentation, user-facing messages, and potentially confusion for existing users
+
+## Action Taken
+
+No code changes required. This document serves as:
+- Evidence of the investigation
+- Documentation of the emoji choice
+- Reference for future contributors
+
+## Alternative Considered
+
+We considered switching to crab emoji (🦀) to be more literal to the name, but determined:
+- The cost of change outweighs the benefit
+- "PicoClaw" is a creative name that doesn't need to match a specific crustacean
+- The lobster emoji has character and makes the brand memorable
+
+## Related
+
+- Issue #578: https://github.com/sipeed/picoclaw/issues/578