docs(releases): v17 page covers the 17.0.0-rc.2 window (#4877)

Release-time curation of the layer-3 platform page for the rc.2 cut, sourced
from the 209 changesets pending since the rc.1 version commit (46 major-class)
and the .objectui-sha pin, which is unchanged at 785b8a5d432c.

Adds a "Landed since 17.0.0-rc.1" section:

- the #4535 dual-source convergence closing all seventeen clusters (C1-C17)
  plus #4537/#4538/#4539 and the #4446 symbol-identity ratchet
- #4001's final batches closing the authorable surface
- the ADR-0049 sweep reaching the driver, datasource and service contracts
- the ADR-0078 completeness gate, its Phase 4 runtime twin, and the #4463
  runtime authoring gate
- ADR-0119 atomicity + migration journal, with ADR-0118's actor contract
- protocol/wire and authoring behaviour changes, the security corrections,
  and the new backend capabilities

Extends the upgrade checklist with the rc.2 migrations, adds two highlights,
and records the window's ADRs and issues in References. Renames the rc.2
subsection headings so they do not collide with the rc.0 section's in the TOC.

Docs-only; releases nothing.


Claude-Session: https://claude.ai/code/session_01AaegKY1Y7GqTb8CKMm5GLC

Co-authored-by: Claude <noreply@anthropic.com>

Author: os-zhuang

.changeset/v17-rc2-release-page.md

@@ -0,0 +1,37 @@
+---
+---
+
+Docs-only: bring the v17 platform release page (`content/docs/releases/v17.mdx`)
+up to date for the **17.0.0-rc.2** cut — the layer-3 "big picture" the
+releases-maintenance playbook compiles centrally at release time, sourced from
+the 209 changesets the window left pending since the `rc.1` version commit (46
+`major`-class, 74 `minor`, 55 `patch`, 34 releasing nothing) and the
+`.objectui-sha` pin, which is unchanged at `785b8a5d432c`.
+
+Adds a **Landed since 17.0.0-rc.1** section covering the window: the #4535
+dual-source convergence closing all seventeen clusters (C1–C17) plus #4537 /
+#4538 / #4539 and the #4446 symbol-identity ratchet; #4001's final batches
+closing the authorable surface; the ADR-0049 enforce-or-remove sweep reaching
+the driver, datasource and service contracts (`DriverCapabilities`,
+`findStream`, `IDataEngine.batch`, the four datasource blocks, `openApi31`,
+`activationEvents`, the standalone `validation` kind, the `job` runtime door,
+`sys_comment.visibility`); the ADR-0078 completeness gate with its Phase 4
+runtime twin and the #4463 runtime authoring gate; ADR-0119 atomicity and the
+migration journal with ADR-0118's actor contract; the protocol/wire and
+authoring behaviour changes (batch row shape, hook and validation predicate
+semantics, `script` nodes, datasource routing); the security corrections
+(`sys_comment` record-level access, the `areas[]` navigation gate, the two
+fail-open area gates, unscoped attachment deletes, analytics scoping, sharing
+withdrawal, OTP hardening); and the new backend capabilities (bulk data event
+contract, client-react bulk hooks, blueprint formula/roll-up declarations,
+analytics correctness).
+
+Extends the upgrade checklist with the rc.2 migrations (spec import-path and
+rename table, datasource and driver cleanups, bulk/batch `atomic` semantics,
+hook and validation predicate behaviour, `script` nodes, standalone validation
+artifacts, jobs, `managedBy: 'system-data'`, app areas, comments,
+`getSuspendedScreen`, runtime metadata writes, and the new completeness
+errors), adds two release highlights, and records the window's ADRs and issues
+in References.
+
+Releases nothing.