Prevent cross-worktree session bleed during managed session resume/load

ROADMAP #41 was still leaving a phantom-completion class open: managed
sessions could be resumed from the wrong workspace, and the CLI/runtime
paths were split between partially isolated storage and older helper
flows. This squashes the verified team work into one deliverable that
routes managed session operations through the per-worktree SessionStore,
rejects workspace mismatches explicitly, extends lane-event taxonomy for
workspace mismatch reporting, and updates the affected CLI regression
fixtures/docs so the new contract is enforced without losing same-
workspace legacy coverage.

Constraint: Keep same-workspace legacy flat sessions readable while blocking cross-worktree misuse
Constraint: No new dependencies; stay within the ROADMAP #41 changed-file scope
Rejected: Leave team auto-checkpoint history as final branch state | noisy/non-lore history for a single roadmap fix
Confidence: high
Scope-risk: moderate
Reversibility: clean
Directive: Preserve workspace_root validation on future resume/load helpers; do not reintroduce path-only fallback without equivalent mismatch checks
Tested: cargo test -p runtime session_control -- --nocapture; cargo test -p rusty-claude-cli resume -- --nocapture; cargo test -p rusty-claude-cli --test cli_flags_and_config_defaults; cargo test -p rusty-claude-cli --test output_format_contract; cargo test -p rusty-claude-cli --test resume_slash_commands; cargo test --workspace --exclude compat-harness; cargo check --workspace --all-targets; git diff --check
Not-tested: cargo clippy --workspace --all-targets -- -D warnings (pre-existing failures in unchanged rust/crates/rusty-claude-cli/build.rs)
Related: ROADMAP #41

rust/crates/rusty-claude-cli/tests/cli_flags_and_config_defaults.rs

@@ -266,7 +266,7 @@ fn command_in(cwd: &Path) -> Command {
 
 fn write_session(root: &Path, label: &str) -> PathBuf {
     let session_path = root.join(format!("{label}.jsonl"));
-    let mut session = Session::new();
+    let mut session = Session::new().with_workspace_root(root.to_path_buf());
     session
         .push_user_text(format!("session fixture for {label}"))
         .expect("session write should succeed");