feat(cli_chat): unified agent panel 2a — ConversationBackend core + history migration

[BunsDev]

Description

What: Sub-phase 2a of the Coven agent-surface reconciliation (design in #204). This lands the shared conversation core + persistence migration that a unified agent panel will sit on — no UI yet, and fully behavior-preserving for the existing cli_chat panel.

Why: CastCodes still has two AI-conversation surfaces (the shipped ai_assistant/Familiar daemon panel and the feature-flagged cli_chat CLI panel). Phase 1 (#201) unified their rendering via agent_transcript. 2a unifies the data model so a single panel (2b–2d) can list, persist, and restore conversations from both backends.

How:

• New ConversationBackend { Cli(AgentKind) | Daemon { harness } }; ChatConversation carries a backend instead of a bare AgentKind.
• sqlite schema v2 adds a chat_conversation.backend column (cli | daemon) via the existing versioned migration; legacy rows backfill to cli.
• Store reads/writes both columns and round-trips Cli/Daemon conversations.
• Non-destructive, idempotent migration of the daemon panel's ~/.coven/stream-history.json into coven-code Daemon conversations (one text blob → one AssistantResponse entry; source file renamed .migrated, never deleted).

Reuses Phase 1's agent_transcript ChatEntry render model. The unified panel view, composer routing, daemon conversation source, entry point, and deprecation are out of scope here — they are 2b–2d (separate plans).

Linked Issue

Continues the reconciliation roadmap (design/spec in #204; Phase 1 shipped in #201). No separate tracking issue, per the #204 precedent.

Testing

• cargo nextest run -p warp-app --features cast-agent -E 'test(cli_chat::)' → 36/36 pass — the full pre-existing cli_chat suite is unchanged (proves the generalization is behavior-preserving), plus new tests: ConversationBackend round-trip, unknown-agent fallback, v1→v2 backend backfill, and history-migration insert + idempotency.
• cargo clippy -p warp-app --features cast-agent --all-targets -- -D warnings clean; cargo fmt -p warp-app -- --check clean.
• ./script/check_ai_attribution, ./script/check_rebrand, ./script/check_cli_chat_boundary pass.
• Not manually run with ./script/run — no user-visible surface in 2a (data layer only).

Agent Mode

• CastCodes Agent Mode — PR via CastCodes. Join OpenCoven on Discord for support.

[Copilot]

Pull request overview

This PR implements Phase 2a’s shared conversation core for cli_chat by introducing a backend discriminator (Cli vs Daemon) into the conversation model, persisting it in sqlite via a schema v2 migration, and adding a non-destructive daemon history import helper (not yet wired into UI startup).

Changes:

• Introduce ConversationBackend and migrate ChatConversation from agent: AgentKind to backend: ConversationBackend.
• Bump sqlite schema to v2 by adding chat_conversation.backend with a default backfill to cli, and update store read/write paths accordingly.
• Add an idempotent helper to migrate ~/.coven/stream-history.json into sqlite as Daemon { harness: "coven-code" } conversations, plus targeted tests.

Reviewed changes

Copilot reviewed 11 out of 11 changed files in this pull request and generated 2 comments.

Show a summary per file

File	Description
app/src/cli_chat/view/model_picker.rs	Switch model-picker labeling to read agent/model from ConversationBackend.
app/src/cli_chat/view/conversation_list.rs	Render conversation titles/subtitles using ConversationBackend display naming.
app/src/cli_chat/store.rs	Persist/load backend alongside legacy agent (now “name”) column; reconstruct backend from both.
app/src/cli_chat/store_tests.rs	Update store tests for ConversationBackend and validate round-trips.
app/src/cli_chat/store_schema.rs	Schema v2: add backend column with default 'cli'.
app/src/cli_chat/store_schema_tests.rs	Add coverage ensuring v1→v2 migration backfills backend = 'cli'.
app/src/cli_chat/model.rs	Update conversation creation to wrap CLI agents in ConversationBackend::Cli.
app/src/cli_chat/mod.rs	Expose new history_migration module.
app/src/cli_chat/history_migration.rs	Add daemon stream-history.json → sqlite migration helper + tests.
app/src/cli_chat/conversation.rs	Add ConversationBackend and parsing helpers; move conversation ownership to backend.
app/src/cli_chat/conversation_tests.rs	Add tests for backend persistence round-trip and unknown-agent fallback behavior.

Comments suppressed due to low confidence (1)

app/src/cli_chat/store.rs:51

• upsert_conversation does not update the persisted agent/backend columns on conflict. If a session_id ever collides across backends (e.g. daemon history migration ID matches an existing CLI session, or a conversation is re-created with a different backend), the row will retain the old discriminator and be reconstructed as the wrong backend on read.

             ON CONFLICT(session_id) DO UPDATE SET
                title      = excluded.title,
                cwd        = excluded.cwd,
                project    = excluded.project,
                updated_at = excluded.updated_at,

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