Channel users get the same context split the desktop popover shows
(PR #54907) — system prompt, tools, rules, skills, MCP, subagents,
memory, conversation — under the existing Context line in /usage.
Reuses agent.context_breakdown.compute_session_context_breakdown, so
there is no new tool and no new engine. The slices are estimates
(chars/4) and the block is labelled _(estimated)_; the headline
Context line keeps using the provider-measured last_prompt_tokens.
Rendering is fail-open: any engine error returns no breakdown and the
rest of /usage is unaffected.
- gateway/slash_commands.py: _context_breakdown_lines() helper + wire
into _handle_usage_command
- locales/*.yaml: breakdown_header, breakdown_line, and 8 category
labels across all 16 locales (parity gate)
- tests/gateway/test_usage_command.py: render + fail-open coverage
6aefc9d925