feat(conversations): add move binding endpoint

[sytone]

Closes #140

Changes

New endpoint: POST /api/conversations/{conversationId}/bindings/{bindingId}/move

Allows moving a channel binding from one conversation to another:

• Removes the binding from the source conversation
• Adds it to the target conversation
• Both conversations saved atomically
• Same-conversation move is a no-op (returns 204)

Request body

{ "targetConversationId": "c_abc123" }

Response codes

• 204 — success (or same-conversation no-op)
• 400 — empty targetConversationId
• 404 — source conversation, binding, or target conversation not found

MoveBindingRequest DTO

Added to ConversationDtos.cs alongside the existing AddBindingRequest.

Tests (6 new)

• Happy path: binding removed from source, appears in target
• Same-conversation no-op: count unchanged, returns 204
• Source not found: 404
• Binding not found: 404
• Target not found: 404
• Empty targetConversationId: 400

All 1642 gateway + 86 CLI + 206 CodingAgent tests pass.

Note: This is the server-side REST API portion of #140. Portal UI (bindings settings panel, drag-to-move) is a follow-up.

[sytone]

Farnsworth Review -- PR #488

CI: All checks passing
Merge conflicts: CLEAN/MERGEABLE
Conventional commit title: feat(conversations): add move binding endpoint -- correct

Test coverage: 6 tests covering happy path, same-conversation no-op, source/binding/target not-found, empty request body. All 1642 gateway + 86 CLI pass.

Spec completeness vs #140: Server-side REST API portion complete. Portal UI noted as follow-up -- acceptable scope split.

Code notes:
Atomic save of both conversations is good defensive practice.
Same-conversation no-op returning 204 is correct REST semantics.
MoveBindingRequest DTO co-located with AddBindingRequest -- sensible.

LGTM. Ready to merge.

[sytone]

CI: All checks passing
Merge conflicts: Clean / MERGEABLE
Commit title: Conventional commit format correct
Coverage: 6 tests covering 204 success, no-op same-conversation, 400/404 sad paths
Spec completeness: Closes partial #140 (move binding endpoint) - POST /api/conversations/{id}/bindings/{bid}/move implemented; portal bindings settings panel noted as follow-up

LGTM - ready to merge.

[sytone]

Farnsworth Review — PR #488

CI: ✅ All checks passing
Merge conflicts: ✅ Clean (MERGEABLE)
Conventional commit title: ✅ feat(conversations): add move binding endpoint

Test coverage:

• ✅ 6 tests (204 success, no-op same-conv, 400 missing target, 404 conv not found, 404 binding not found)
• 1642/1642 pass

Spec completeness vs #140 (partial): REST endpoint implemented. Portal UI (bindings settings panel) correctly deferred to PR #493.

LGTM. Ready to merge.

[sytone]

Closing as part of a planned hard-reset of the in-flight branch set so the new domain-model refactor can land on a clean trunk.

Audit verdict: close

Rationale: ChannelBinding shape changes in Phase 6b (ThreadId removed; composite ChannelAddress). Re-add the endpoint on the new shape.

The new plan (in session state) reshapes core types: Citizen (User+Agent union), Vogen-generated value objects, ThreadId removed in favour of composite ChannelAddress, mark-not-delete compaction, centralised SessionContextProjector, single-path routing. Many in-flight branches touch contracts that are about to change — rebasing later would be more work than rebuilding on the new shape.

If this work is still wanted, refile as a new issue/PR against the post-refactor contracts.