iter cli-diag-human: route WorkspaceLoadError through diagnostic in non-JSON path

Closes P2 todo "CLI human-mode diagnostic surface for
WorkspaceLoadError" surfaced by ct.1.8 tester (2026-05-11).
Pre-iter, non-JSON `ail check` (+8 sibling subcommands) propagated
loader errors via anyhow's Display, producing
`Error: <message>` without the bracketed `[code]` prefix the JSON
path emits.

Fix: new private helper `load_workspace_human(path)` in
crates/ail/src/main.rs that wraps ailang_surface::load_workspace,
threads any WorkspaceLoadError through workspace_error_to_diagnostic,
formats the resulting Diagnostic into a single stderr line
`error: [<code>] <def>: <message>`, and exits non-zero. Pure I/O
errors still propagate as anyhow errors.

Nine call sites swapped to the helper (check non-JSON arm, build,
run, emit-ir, prose, describe, deps, diff, manifest). The JSON arm
of `ail check` keeps its explicit `match` — different output
contract (structured stdout array).

The BareCrossModuleTypeRef Diagnostic message gained the existing
migration-command hint ("Run `ail migrate-canonical-types` to fix
legacy fixtures.") so the ct.1.8 actionable-hint test stays green.
The hint previously rode on WorkspaceLoadError's thiserror Display;
making workspace_error_to_diagnostic the single source for both
JSON and human paths required moving it into the Diagnostic body.

RED test crates/ail/tests/cli_diag_human_workspace_load_error.rs
pins the bracketed-code surface on a missing-import workspace
(tempdir-based fixture; no committed corpus addition).

cargo test --workspace: 565/0/3. clippy + doc: zero warnings.
Roadmap entry struck.

docs/journals/2026-05-14-iter-cli-diag-human.md

@@ -0,0 +1,72 @@
+# iter cli-diag-human — non-JSON CLI surfaces `WorkspaceLoadError` with bracketed `[code]`
+
+**Date:** 2026-05-14
+**Started from:** 6755060 (post-rpe.1.tidy)
+**Status:** DONE
+
+## Summary
+
+Closes the P2 todo "CLI human-mode diagnostic surface for
+`WorkspaceLoadError`" surfaced by the ct.1.8 tester (2026-05-11).
+Pre-iter, the non-JSON path of every CLI subcommand that called
+`ailang_surface::load_workspace(&path)?` propagated the error via
+anyhow's Display — producing `Error: <thiserror-formatted-message>`
+on stderr — while the JSON path of `ail check --json` correctly
+routed through `workspace_error_to_diagnostic` and emitted the
+bracketed `[code]` prefix. The asymmetry made the human-mode
+output harder to triage and less consistent across the toolchain.
+
+Fix: new private helper `load_workspace_human(path) -> Result<Workspace>`
+in `crates/ail/src/main.rs` that wraps `ailang_surface::load_workspace`,
+threads any `WorkspaceLoadError` through the existing
+`workspace_error_to_diagnostic`, formats the resulting `Diagnostic`
+into a single stderr line of shape
+`error: [<code>] <def>: <message>`, and exits non-zero. Pure I/O
+errors (where `workspace_error_to_diagnostic` returns `None` per
+the loader's own contract) still propagate as anyhow errors so the
+caller's `?`-flow stays well-behaved.
+
+Nine call sites in `main.rs` swapped from
+`ailang_surface::load_workspace(<expr>)?` to
+`load_workspace_human(<expr>)?`: the `ail check` (non-JSON arm),
+`build`, `run`, `emit-ir`, `prose`, `describe`, `deps`, `diff`,
+`manifest` paths. The JSON arm of `ail check` (line 596) kept its
+explicit `match` shape — it builds a structured diagnostics array
+on stdout, which is a different output contract.
+
+The `BareCrossModuleTypeRef` arm of `workspace_error_to_diagnostic`
+gained the existing migration-command hint
+("Run `ail migrate-canonical-types` to fix legacy fixtures.") so
+that the ct.1.8 actionable-hint test
+(`check_human_mode_emits_actionable_message_to_stderr`) stays
+green. The hint was previously carried by `WorkspaceLoadError`'s
+thiserror Display impl; making `workspace_error_to_diagnostic` the
+single source for both JSON and human paths required moving it
+into the Diagnostic message body.
+
+## Files touched
+
+- `crates/ail/src/main.rs` — new `load_workspace_human` helper
+  (~25 lines, including doc comment); 9 call-site swaps; one
+  Diagnostic message gained the migration-hint suffix.
+- `crates/ail/tests/cli_diag_human_workspace_load_error.rs` —
+  new RED-pin test (tempdir-based fixture asserting
+  `[module-not-found]` in stderr on a missing-import workspace).
+- `docs/roadmap.md` — entry struck through.
+
+## Verification
+
+- RED test `check_non_json_emits_bracketed_module_not_found`
+  flipped from RED to GREEN.
+- `cargo test --workspace` → 565 / 0 / 3 (was 564 pre-iter; +1
+  from this iter's RED pin).
+- `cargo clippy --workspace --all-targets` → 0 warnings.
+- `cargo doc --workspace --no-deps` → 0 warnings.
+
+## Concerns
+
+- (none)
+
+## Known debt
+
+- (none)