refactor(session): nuke dead sessionParams / sessionDisplayId pipeline (v43)

These columns and the messages that plumbed them existed for the CLI-
adapter era — Gemini's resume id and provider-specific session params
rode the run-finished envelope back onto the session row so the next
turn could resume. Pi Mono dispatches every provider through pi-ai and
emits neither value. The worker has been posting literal null on every
finish, finalizeRun has been writing null into task_sessions, and
rotateSession has been carrying null forward.

Remove the wire, the writer, the carry-forward, and the columns:

  - v43 migration rebuilds task_sessions without session_params_json /
    session_display_id, and runs without session_display_id. Follows
    the idempotent "create new, copy, swap, reindex" pattern used by
    v41. context_snapshot_json is preserved (also unreferenced today
    but outside this cleanup's scope).
  - RunJob / EnqueueRunPayload / ChildMessage / worker-types zod
    schema no longer carry the fields. finishRun() / createNewSession()
    signatures tighten in lockstep.
  - rotateSession starts the new session with fresh counters and no
    carry-forward.
  - turn-context resolveSession returns just the session id.
  - TaskSessionRecord / RunRecord lose the dead fields.

498/498 unit tests pass. typecheck + build clean.

tests/unit/edge-case-session.test.ts

@@ -118,8 +118,6 @@ describe("Edge Case: Session Rotation During Execution (D-05.3)", () => {
       companyId,
       agentId,
       adapterType: "gemini-cli",
-      sessionParamsJson: null,
-      sessionDisplayId: null,
     });
 
     // Simulate runs until we reach the maxRuns threshold (20)
@@ -146,8 +144,6 @@ describe("Edge Case: Session Rotation During Execution (D-05.3)", () => {
       companyId,
       agentId,
       adapterType: "gemini-cli",
-      sessionParamsJson: null,
-      sessionDisplayId: null,
     });
 
     // Accumulate tokens past the threshold in one big call
@@ -172,8 +168,6 @@ describe("Edge Case: Session Rotation During Execution (D-05.3)", () => {
       companyId,
       agentId,
       adapterType: "gemini-cli",
-      sessionParamsJson: null,
-      sessionDisplayId: null,
     });
 
     // Accumulate enough to trigger rotation
@@ -197,7 +191,6 @@ describe("Edge Case: Session Rotation During Execution (D-05.3)", () => {
       exitCode: 0,
       signal: null,
       model: "gemini-pro",
-      sessionDisplayId: null,
       unattributedCost: false,
     });
 
@@ -229,8 +222,6 @@ describe("Edge Case: Session Rotation During Execution (D-05.3)", () => {
       companyId,
       agentId,
       adapterType: "gemini-cli",
-      sessionParamsJson: JSON.stringify({ resumeKey: "abc" }),
-      sessionDisplayId: "gemini-session-1",
     });
 
     // Add usage to the old session
@@ -244,8 +235,6 @@ describe("Edge Case: Session Rotation During Execution (D-05.3)", () => {
       companyId,
       agentId,
       adapterType: "gemini-cli",
-      sessionParamsJson: JSON.stringify({ resumeKey: "abc" }),
-      sessionDisplayId: "gemini-session-2",
     });
 
     // Get the new active session
@@ -268,8 +257,6 @@ describe("Edge Case: Session Rotation During Execution (D-05.3)", () => {
       companyId,
       agentId,
       adapterType: "claude-pro",
-      sessionParamsJson: null,
-      sessionDisplayId: null,
     });
 
     // Accumulate way past all thresholds
@@ -292,8 +279,6 @@ describe("Edge Case: Session Rotation During Execution (D-05.3)", () => {
       companyId,
       agentId,
       adapterType: "openai-codex",
-      sessionParamsJson: null,
-      sessionDisplayId: null,
     });
 
     // Accumulate way past all thresholds
@@ -317,8 +302,6 @@ describe("Edge Case: Session Rotation During Execution (D-05.3)", () => {
       companyId,
       agentId,
       adapterType: "gemini-cli",
-      sessionParamsJson: null,
-      sessionDisplayId: null,
     });
     db.incrementSessionUsage(sessionId, 300000, 200000, "run-1");
 
@@ -338,7 +321,6 @@ describe("Edge Case: Session Rotation During Execution (D-05.3)", () => {
       exitCode: 0,
       signal: null,
       model: "gemini-pro",
-      sessionDisplayId: null,
       unattributedCost: false,
     });