Cross-repo workflow grouping: entity, persistence, MCP

[jbachorik]

A single piece of work — a feature, a refactor, a bug hunt — often spans sessions across several repositories. Today the only link between them is the operator's memory; there is no object that says "these sessions are one workflow," and no shared context that survives a session's context being cleared.

This change introduces a first-class Workflow entity that groups related sessions across repositories and carries a shared brief: the running narrative of the whole effort, written by whichever member session is active and read by the next one opened in any repo. It is the layer above forkedFrom (dead code, never set) and the per-session HandoffBrief (one session's testimony to its in-place successor).

Domain

New records: WorkflowId, WorkflowStatus (OPEN | ARCHIVED), WorkflowBrief, Workflow. WorkflowBrief reuses the HandoffBrief shape minus sessionId (workflow-scoped, not session-scoped) and writtenAtCommit (a workflow spans multiple repos and branches, so a single HEAD is meaningless). ManagedAgentSession gains an optional workflowId (14th field, at-most-one workflow per session). ApplicationState gains a workflows list. All follow the existing record/id/with* patterns.

Persistence

ApplicationStateCodec encodes/decodes the workflows array and the session workflowId leniently — a missing or malformed workflows array recovers to empty, a missing workflowId recovers to Optional.empty(). No schema version bump, the same discipline used for forkedFrom/evalMode when they were added.

Service

SessionManager gains workflow CRUD: createWorkflow, renameWorkflow, setWorkflowStatus, deleteWorkflow, writeWorkflowBrief, setSessionWorkflow, touchWorkflow, applyAgentWorkflowHandoff. prepareSuccessorSession copies workflowId from the outgoing session alongside the fields it already copies (displayName, namePinned, worktreeRoot, branchCreatedHere, evalMode) — a one-line addition, not riding forkedFrom.

MCP

session_handoff gains an optional workflow: true flag that writes the calling session's workflow brief instead of its per-session brief. Refused if the session is not a workflow member. No agent-driven workflow creation — naming the effort is a human act, like naming a session.

Design decisions

• Single authored brief, not a roll-up of member briefs — one narrative, replaced wholesale.
• At most one workflow per session — to join a second effort, fork the session into the second workflow.
• Fork offers three destinations: same-workflow (default if affiliated; brief linked, not copied into the seed), new-workflow, or no-workflow. The per-session brief seed is unchanged in all three cases.

Verification

compileJava + compileTestJava pass. 6 new tests pass: 4 codec round-trip tests (workflow, session-with-workflowId, old-state-without-workflows, old-session-without-workflowId) and 2 MCP tests (workflow-target-writes-workflow-brief, absent-flag-writes-per-session-brief). One pre-existing test failure (adoptingARemoteOnlyBranchMintsATrackingLocalBranchAndReportsBothNames) fails on main at 9a1b84b — a git worktree add environment issue, unrelated to this change.

Not yet implemented

The UI layer — workflow grouping in the session rail, archived-workflow filter toggle, and workflow brief edit dialog. That is the next chunk of work.

Design doc: docs/plans/workflow-grouping-design.md.