feat(cli): status line should degrade gracefully when ctx/token usage is unavailable

[me2seeks]

Context

The TUI status line already implements a token/context segment (#1067): ctx used/window pct% (yellow >80%, red >95%), plus $cost and cache % in renderMakaPiStatusLine (packages/cli/src/pi-transcript.ts).

However, the segment is silently absent unless ALL of these hold:

• the connection's selected model has a resolvable contextWindow (declared via relay profile, connection model list, or static metadata), and
• the provider reports per-step input tokens so the runtime can emit contextRemaining in token_usage (ai-sdk-backend.ts), and
• at least one turn has completed.

Observed on an opencode-go connection: Maka · Full access · muse-spark-1.2-contributor · opencode-go · ~/project/maka-agent — no ctx, no cost. The user cannot tell whether the connection doesn't report usage, the model lacks a declared context window, or just no turn has finished yet.

Reference: pi's footer design (badlogic/pi-mono)

pi's interactive footer (packages/coding-agent/src/modes/interactive/components/footer.ts) always renders a context segment and degrades explicitly:

• pct%/window with color thresholds (warning >70%, error >90%)
• fallback ?/200k when usage is unknown but the window is known
• cumulative ↑in ↓out R/W CH% $cost stats alongside

Proposal

1. When modelContextWindow is known but contextRemaining is not yet available (fresh session / provider doesn't report usage), render ctx ?/<window> (dim) instead of nothing.
2. When neither is known, keep the segment hidden (current behavior) — no window to anchor a fallback.
3. Follow-up: verify whether the opencode-go relay reports per-step input tokens; if it does but contextRemaining still isn't emitted, fix that path.

Acceptance criteria

• A session on a connection with a known context window shows ctx ?/<window> before the first completed turn, and ctx used/window pct% after.
• Existing color thresholds and the omit-when-unknown-window behavior are unchanged.

[me2seeks]

I'm working on this issue.