EstimatedCostUSD multiplies the cumulative usage by the current model's per-million-token rates. Returns -1 for an unknown model.

PrintBanner renders the startup banner. Falls back to a single-line wordmark when the terminal is narrower than the big banner needs.

ReadChatInput shows the bordered input box and blocks until the user submits or hits ctrl-d. Returns (text, ok). ok=false on exit.

Send returns the next canned response (or Err, or a default end_turn), recording the messages and tools it was called with for later assertion.

Send appends a user message and runs the tool-use loop until the model stops requesting tools (or MaxTurns is reached). Returns the final assistant te

SentAt returns a copy of the messages passed to the i-th Send call. Indexing is 0-based and matches the order of Responses. Returns nil when i is out

StartSpinner begins a braille spinner on stdout with the given label. No-op when stdout isn't a TTY (piped, redirected). Call Stop() to clear.

Definitions must be sorted by name. Two reasons matter — chapter 09's "map iteration is random" warning, and prompt caching (chapter 17), which silent

Tools that fail report it via the (result, isErr) channel rather than a Go error — the agent loop relies on this contract (chapter 02).

Latest walks back from the newest event to find one with a non-empty payload, skipping payload-less events along the way.

Unpaired events return (zero, false). The lookup must not match itself.

Pair walks both directions: a request emits → response correlates back. Calling Pair on either ID returns the other.

All tests in this file share the package's global state (the ring, the nextID counter, the sink). They run sequentially (no t.Parallel()) and reset st

The ring drops the oldest event once it reaches capacity. We push more than the ring can hold and verify the front is gone, the back is intact, and Fi

When the desired split already lands on a clean user text message, SafeSplitPoint returns it as-is.

Edge values bounce out without walking the slice.

If no clean boundary exists in the prefix, returns 0 — "do nothing" is safer than risking an orphaned tool_use.

When desired falls inside a tool_use/tool_result pair, the function walks back to the previous clean user-text boundary.

TestSendLoopsOnToolUse covers the tool-use round-trip: the model asks for `echo`, the agent dispatches it, the agent loops back to the model with the

TestSendPropagatesProviderError makes sure a provider failure bubbles out of Send instead of being swallowed. The error itself should be the exact sen

TestSendReturnsTextOnEndTurn exercises the simplest path: the model replies with a text block and a non-tool stop reason, and Send returns that text t

TestSendStopsAtMaxTurns confirms the safety clamp: a provider that keeps requesting tools indefinitely is bounded by Agent.MaxTurns. The loop terminat

Empty sessions shouldn't leak into the index — opening, doing nothing, and closing leaves the store untouched.

If the session file referenced in index.json was deleted manually, the loader should prune the dead reference on the next open.

Recall is matched by tag OR summary substring.

After a session is closed, reopening the store should re-load the index and surface the previous session via Preamble and Recall.

The sink is called once per Record while enabled, in order, with the fully-constructed Event.

Above the keep-window: drops a prefix, snapping to a safe boundary.

Below the keep-window: no-op.

The whole point of SafeSplitPoint is that compaction never separates a tool_use from its tool_result. This is a regression test for that invariant on

Subset of nothing is a valid empty registry — used by subagents that shouldn't have any tools at all.

TotalUsage returns the cumulative tokens this provider has consumed since it was constructed. Subagents that share the provider contribute to the same

WithLogging is sugar for &LoggingStrategy{Inner: inner, FilePath: path}.

cmdSubagents lists registered subagent types and, separately, any that are currently running. The active list is empty when nothing is in flight.