/archon-upgrade Step 1 reads a permission denial as a missing Archon binary

What happened

Found 2026-08-20 during #381's Consumer close-out run (DXP-DesignSystem, plugin 0.23.0, WI 42952). A claude -p run starts in a restrictive permission mode; the shell denied archon --version, and /unic-archon-dlc:archon-upgrade Step 1 reported "Archon is unusable at all" — the verdict for a missing binary, when the binary was present and the command merely refused.

Not a silent failure — the command took its documented branch and reported honestly. But that branch reads "the command is not found, or fails for any other reason", so a permission denial is indistinguishable from a broken install, and the operator gets a confident wrong diagnosis.

Acceptance criterion

Step 1's cannot-run branch tells the operator to check for a permission denial before believing the missing-binary verdict — one line, in the command's own prose. Checked by reading commands/archon-upgrade.md.

Context

The workaround is recorded in the Consumer (DXP-DesignSystem/docs/agents/unic-archon-dlc.md); the fix belongs here. Evidence chain on #381's close-out report (orchestrator session, 2026-08-20 15:54).

Open commands/archon-upgrade.md and read Step 1's cannot-run branch. Update that branch's prose to tell the operator to check for a permission denial before concluding that the Archon binary is missing; completion is verified by reading the updated command text.