[samgbafa]

Release 1.21.6 from main 3bac5aa (#389 and #302). Bumps tinycloud-node-server/Cargo.toml, Cargo.lock, test/m1-realdata-e2e/Cargo.lock and test/w5-policy-runtime-node-e2e/Cargo.lock from 1.21.5 to 1.21.6, and moves [Unreleased] under [1.21.6] - 2026-10-21 (the Changes lines unchanged, a Release notes block added). No database migrations. Version is manual per docs/releasing.md.

Details: TC-1581, TC-735

[samgbafa]

APPROVE: see TC-1581 (reviewed exact head dabd6b3)

Mechanical release check, read-only:

• 5 files changed, each a single version line (tinycloud-node-server/Cargo.toml, the three Cargo.lock tinycloud-node entries, CHANGELOG.md). No other version or dependency lines.
• behind_by 0 vs main (3bac5aa).
• CHANGELOG: [Unreleased] empty; [1.21.6] - 2026-10-21 has ### Release notes then ### Changes; the ### Changes block is byte-identical to main's former [Unreleased] body; everything from ## [1.21.5] down is byte-identical to main.
• Release notes: behaviour only, no weakness/incident/bypass wording. Non-blocking nit: the last bullet ("No database migrations. Rollback is the 1.21.5 image…") has no Details: TC-N; same pattern as 1.21.5, so left as-is.
• CI at head: all required checks pass (fmt, clippy, build, build (workspace), test (workspace, PostgreSQL-backed), at-rest harness, m1-realdata, w5 lockfile, separate lockfiles, Version guard, capabilities, plan, Build dstack ingress image). Release/deploy jobs skipped.