fix(zsh): harden _radian_version_check against a contaminated version cache

.STATUS

@@ -959,25 +959,24 @@ the 2026-09-12 session block above.
 **Issue #275 shipped and closed (2026-09-13)** — `teach dashboard`, PR #522 merged to `dev`. See
 the 2026-09-13 session block above.
 
-1. **Issue #487** — AI rewrite trigger (`:rw`/`:rwq`): unbuilt, spec lost, four decisions
-   preserved in the issue body. Needs a re-written spec before any implementation.
-2. **Markdown-lint backlog** (advisory, non-blocking by design) — 394 errors, 138 of them MD040
+1. **Markdown-lint backlog** (advisory, non-blocking by design) — 394 errors, 138 of them MD040
    (fenced blocks needing a language tag). `test.yml` documents why it stays advisory; clearing it
    is the precondition for making that gate blocking.
-3. **Decide the fate of `feature/email-dispatcher-restructure`** — either merge its ORCHESTRATE
+2. **Decide the fate of `feature/email-dispatcher-restructure`** — either merge its ORCHESTRATE
    plan's substance somewhere durable, or retire the branch deliberately. Left standing 2026-09-05
    because it is the only copy.
+   because it is the only copy.
 
 ## Parked
 
 - API documentation push (50% → 80% coverage of 348 functions) — parked 2026-07-02, no active driver
-- ~~Code workspace manager (`code ws` dispatcher)~~ — retired 2026-07-02, spec moved to `docs/specs/_archive/SPEC-code-workspace-2026-02-13.md` (never implemented, no demand signal in 4.5mo)
 - **Issue #517** — historical `DC_API_KEY` exposure — parked 2026-09-13, nothing actionable left (provider unidentified, no consumer, no live credential to rotate; history-scrub deferred)
+- **Issue #487** — AI rewrite trigger (`:rw`/`:rwq`) — parked 2026-09-14 by user decision (worth-it review done: real recurring friction, moderate effort, low risk, but not prioritized now). Spec lost, four architecture/backend decisions preserved in the issue body; needs a fresh spec, not a resume, whenever picked back up.
 
 ---
 
-**Last Updated:** 2026-09-13
-**Status:** v7.17.3 released and tagged (2026-09-09/10) | `dev` ahead of `main` by `teach check` (#359, PR #519) + `teach week` fix (#521) + `teach dashboard` (#275, PR #522, squash-merged `43493df`) | 0 open PRs | 1 open issue (#487) + 1 parked (#517) | full suite (ZDOTDIR-isolated) — 86 passed / 2 failed (test-atlas-contract, e2e-em-dispatcher — pre-existing external-tool drift, reproduced on `dev` baseline, unrelated to this diff) / 0 timeout across 86 registered suites | man-page guard passing | markdown lint ADVISORY and failing by design (394 errors) | 14 dispatchers + `at` bridge (`teach dashboard` is a new subcommand, not a new dispatcher) | 179 `test-*.zsh` suite files
+**Last Updated:** 2026-09-14
+**Status:** v7.17.3 released and tagged (2026-09-09/10) | `dev` ahead of `main` by `teach check` (#359, PR #519) + `teach week` fix (#521) + `teach dashboard` (#275, PR #522, squash-merged `43493df`) | 0 open PRs | 0 open issues | 2 parked (#487, #517) | full suite (ZDOTDIR-isolated) — 86 passed / 2 failed (test-atlas-contract, e2e-em-dispatcher — pre-existing external-tool drift, reproduced on `dev` baseline, unrelated to this diff) / 0 timeout across 86 registered suites | man-page guard passing | markdown lint ADVISORY and failing by design (394 errors) | 14 dispatchers + `at` bridge (`teach dashboard` is a new subcommand, not a new dispatcher) | 179 `test-*.zsh` suite files
 ## wins: Fixed the regression bug (2026-07-06), --category fix squashed the bug (2026-07-06), fixed the bug (2026-07-06), Fixed the regression bug (2026-07-06), --category fix squashed the bug (2026-07-06)
 ## streak: 1
 ## last_active: 2026-07-06 12:53

zsh/.zshrc

@@ -1116,14 +1116,24 @@ fi
 # If R was upgraded since last shell start, warn user to rebuild radian
 _radian_version_check() {
     command -v R >/dev/null 2>&1 || return 0
-    local r_ver cached cache_dir
+    local r_ver cached cache_dir old
     r_ver=$(R --version 2>/dev/null | head -1 | awk '{print $3}')
+    # Guard against a malformed R --version parse, AND against radian's own
+    # "0.6.x"-style version string ending up here by mistake (both are valid
+    # X.Y.Z shapes, so a plain semver regex can't tell them apart -- R has not
+    # shipped a major version 0 or 1 release in decades, radian has never left
+    # major version 0, so major >= 2 is the actual discriminator).
+    [[ "$r_ver" =~ ^([1-9][0-9]+|[2-9])\.[0-9]+\.[0-9]+$ ]] || return 0
     cache_dir="${HOME}/.cache"
     cached="${cache_dir}/radian_r_version"
     mkdir -p "$cache_dir"
     if [[ -f "$cached" ]]; then
-        local old=$(cat "$cached")
-        if [[ "$old" != "$r_ver" ]]; then
+        old=$(cat "$cached")
+        # Only warn if the cached value is itself a plausible R version -- a
+        # stale/contaminated cache entry must not be compared against the real
+        # R version, or the warning is nonsense (this is exactly how a past
+        # version of this check produced "R changed: 0.6.16 -> 4.6.1").
+        if [[ "$old" =~ ^([1-9][0-9]+|[2-9])\.[0-9]+\.[0-9]+$ && "$old" != "$r_ver" ]]; then
             print -P "%F{yellow}⚠️  R changed: ${old} → ${r_ver}. If radian breaks, run: pipx reinstall radian%f"
         fi
     fi