feat(tui): show session cost in tray status line

[Xsidz]

Summary

Shows accumulated session spend in the TUI tray/status line next to the existing token/context readout:

main · 128.4k (61%) · $1.32

• Added sessionCost?: number to AgentConnectionState in types.ts
• Populated from session.getSessionStats().cost in createAgentConnectionState (snapshot.ts) so cost is available immediately on attach
• Persisted each turn via refreshConnectionContextUsage alongside the existing contextUsage patch (no extra RPC call — getSessionStats was already called here and the result discarded)
• Rendered in getTrayContextLabel with sub-cent precision: 4 decimal places for cost < $0.01 (e.g. $0.0042), 2 decimal places otherwise

All the plumbing already existed; this is a display-only change.

Test plan

• npm run check passes (biome, tsgo, installer render, browser smoke)
• $0.00 shown when cost is 0 (before first assistant turn)
• Sub-cent cost shows 4 decimal places (e.g. $0.0042)
• Normal cost shows 2 decimal places (e.g. $1.32)
• Cost only appears when sessionCost is populated (no undefined rendered)

Fixes #894

Note

Show session cost in TUI tray/status line alongside token/context readout

• Adds an optional sessionCost field to AgentConnectionState in types.ts, populated from session.getSessionStats() in snapshot.ts.
• Extends getTrayContextLabel in interactive-mode.ts to append a formatted cost string (e.g. $1.32) next to the context usage label, updated after each completed turn.
• Adds formatSessionCost helper: shows $0.00 for zero, 4 decimal places below $0.01, otherwise 2 decimal places.

^{Macroscope summarized 23d7315.}

[Copilot]

Pull request overview

Adds persistent session cost visibility to the interactive TUI tray/status line by plumbing SessionStats.cost into the connection snapshot/state and rendering it next to the existing token/context usage readout.

Changes:

• Extended AgentConnectionState with optional sessionCost?: number.
• Populated and refreshed sessionCost from getSessionStats().cost (on attach via snapshot, and after each completed turn via the existing context-usage refresh).
• Rendered a cost label in the tray with sub-cent precision rules and documented the change in the coding-agent changelog.

Reviewed changes

Copilot reviewed 4 out of 4 changed files in this pull request and generated 1 comment.

File	Description
packages/coding-agent/src/modes/interactive/interactive-mode.ts	Persists sessionCost during usage refresh and appends a formatted cost label to the tray context string.
packages/coding-agent/src/modes/agent-connection/types.ts	Adds sessionCost?: number to the connection state shape.
packages/coding-agent/src/modes/agent-connection/snapshot.ts	Populates sessionCost from session.getSessionStats() so it’s available immediately on attach.
packages/coding-agent/CHANGELOG.md	Adds an Unreleased entry documenting the new tray cost display.

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[Xsidz]

Good catch — fixed in a82fb3ca. Replaced session.getContextUsage() with sessionStats.contextUsage since getSessionStats() already calls getContextUsage() internally.