[jefft72]

Summary

Teaches AgentSession to enter and leave plan mode safely, swap its tool registry while planning, and hand back a one-shot continuation when a plan is accepted.

Replaces #64, which could not build against main.

Reasoning

Plan mode changes what the agent is allowed to do, so the transition needs to be refused while work is in flight rather than applied optimistically.
A submitted plan also has to be resolved before the session can return to default mode, otherwise an accepted plan could be silently abandoned.

The accepted plan is handed back as an opaque, single-use continuation rather than a plain string.
That lets the session reject stale or replayed tokens and bypass command, template, and input transformation for a handoff it already trusts.

The canonical read-only tools exposed while planning are built-ins, so a caller that disables built-ins must not get them back through plan mode.
The session now carries that decision explicitly and leaves submit_plan as the only planning tool in that case.

Changes

• Adds setCollaborationMode with idle, queue, and pending-plan guards, plus persisted mode transitions
• Swaps the tool registry for a plan-scoped one while planning, keeping submit_plan intrinsic
• Adds resolvePlan, pendingPlan, pendingPlanContinuation, and promptPlanContinuation with stale-token rejection
• Adds builtinToolsDisabled so planning honours --no-tools builtin
• Fixes a stray closing brace in setActiveToolsByName that prevented the file from parsing
• Removes a dead call to the profile-only compaction instructions helper

Testing

• npx vitest --run test/suite/agent-session-plan-mode.test.ts test/plan-mode-tools.test.ts test/compaction.test.ts
• tsgo --noEmit reports zero errors
• biome check . clean

[Issacboy123]

LGTM! Cleanly puts plan lifecycle, persistence, and tool policy in the session layer. It also preserves a disabled built-in tool policy while plan mode is active, which avoids reopening access through the new mode. Didn't find any significant issues in review.