fix(xce-test-cli-ux): fix bug-1557's join maxmem default

cmd_join_worker's simulated-worker maxmem default was 64 bytes -- a
leftover from when the field was MB-scale, unfixed when maxmem became
bytes-canonical elsewhere. Now 64 * 1024 * 1024. Extracted the
argument-parsing/defaulting logic into join_worker_parse_attrs()
(join_worker_args.c), since it runs entirely before the function's
network call and is a genuine testable seam -- same precedent as
task 2.5's joblist_display.c. Verified live against a real deployed
cluster (workerlist reports MaxMem: 64.00 MB) plus a permanent 5-test
regression suite. maxswap/maxtmp have the identical stale-default bug
(logged as bug-1793) but are deliberately left unfixed here since
USAGE_JOIN_WORKER's help text currently documents their stale values
accurately -- fixing only the code would create a new docs mismatch;
a locked-in sibling-defaults test documents this for the follow-up.
1353/1353 across the full controller suite (+5), 0 regressions.

Task 2.6 of .kiro/specs/xce-test-cli-ux/tasks.md.
Requirements: 12.1

Co-Authored-By: Claude Sonnet 5 <noreply@anthropic.com>
Claude-Session: https://claude.ai/code/session_019jaMf9QEwpugH2W9KAuc7f

.kiro/specs/xce-test-cli-ux/tasks.md

@@ -91,7 +91,7 @@
   - _Requirements: 11.1, 11.3, 11.4, 11.5, 11.6, 11.7, 11.8_
   - _Boundary: Bug-1711 Fixes_
 
-- [ ] 2.6 (P) Fix bug-1557's join maxmem default
+- [x] 2.6 (P) Fix bug-1557's join maxmem default
   - Correct the simulated worker-join command's default memory value to the codebase's current bytes-canonical convention
   - Observable completion: joining a simulated worker without specifying memory reports the corrected byte-scale default instead of the stale value
   - _Requirements: 12.1_
@@ -178,6 +178,7 @@
 ## Implementation Notes
 - `src/tools/xce-build.sh controller asan xce.build --incremental` writes its build dir at `src/xce.build/` (relative to the script's own location), not a repo-root `xce.build/` — meson logs are at `src/xce.build/meson-logs/testlog.txt`. (task 1.1)
 - New Unity test files need two wiring points, not just meson.build's source list: also register an `extern void test_<module>(void);` + `TEST(test_<module>);` in `src/controller/testsuite/controller_test.c`, mirroring the existing `test_rcfile` registration, or the suite silently never runs. (task 1.1)
+- `cmd_join_worker`'s sibling fields `maxswap`/`maxtmp` have the exact same stale-MB-scale bug as bug-1557's `maxmem` (1024/2048 bytes instead of KB/MB-appropriate values) but were deliberately left unfixed here: `USAGE_JOIN_WORKER` currently documents these exact stale values accurately, so fixing only the code would create a new code/docs mismatch outside this task's mandate. Worth a coordinated follow-up bug fixing both fields' defaults and their help text together. A new `test_join_worker_sibling_defaults_unchanged` test locks in today's values so that follow-up isn't confused with this task's maxmem-specific assertions. (task 2.6)
 - When a fix touches a pure function stuck inside `test.c` (no networking/REPL/global-state dependency), extract it into its own module with a standalone meson `test()` target rather than settling for a throwaway/manual verification — this codebase already has two precedents for exactly this (`resval_typeresolve.c`, `misc.c`'s runusage helpers; now also `joblist_display.c` for `worker_status_str`/`job_state_str`/`format_job_time`). `test.c` itself is never linked into `controller_unit_test`, so this extract-to-standalone-module pattern is the only way to get permanent automated coverage for such functions — a scratch/deleted verification harness is not sufficient and will be sent back on review. `cmd_reslist`/`joblist_query`/`cmd_getconf`'s table-printing bodies remain genuinely untestable without a live cluster (fetch+print are inlined together, confirmed on review) and stay uncovered by permanent tests for now. (task 2.5)
 - `cmd_source` translates `rcfile_load`'s raw positive "aborted" return to `-1` rather than forwarding it verbatim, because `preprocess_and_run` only treats a *negative* return as failure (`if (rc < 0)`) — forwarding the raw positive value would let an enclosing `source` line silently read a transitively-aborted nested source as success. No test yet exercises this specific nested-abort-propagation case (all 3 required scenarios pass either way) — worth a dedicated test in Validation phase (4.3 or nearby). (task 2.4)
 - libedit (this project's pinned NetBSD libedit 3.1) provides GNU-readline-compatible `rl_attempted_completion_function`/`rl_completion_matches` verbatim — confirmed against the actual linked header, not assumed. An ambiguous match needs a SECOND consecutive Tab to list candidates (standard readline/bash double-Tab convention) — later black-box tests using Tab must account for this. Also: `test_test_cli.c`'s `clitest_spawn()` disabling kernel ECHO also silently suppressed libedit's own completion feedback in this libedit build (bug-1792) — use the new `clitest_spawn_ex(sess, path, argv, disable_echo)` with `disable_echo=false` for any future test that needs to observe libedit UI behavior (completion, etc.), not just raw command output. (task 2.3)