[schlessera]

Closes #3151
Refs #3150

What changed

This PR lands batch 1 of epic #3150 (epic/3150-attachments) on main:

Sub-PR	Issue	Squash on epic
#3301	#3151	4cd19855219c8bcdfafb8a1104161a90093c5796

• docs(plans): design generic chat attachment intake, ownership and on-demand reading #3301 (spike, docs only): docs/plans/chat-attachments.md designs generic chat attachment intake, ownership and on-demand reading.

This PR adds nothing beyond it, apart from merge commit b741ae0ad, which brings origin/main (90aebd916) into the epic. One conflict, in docs/plans/README.md: main had retired shipped plans and added an Open work column. The resolution keeps main's table and adds the chat-attachments.md row, owned by #3150.

Why this shape

This follows the maintainer ruling of 2026-11-02 for the 0.45.0 epic run, under which each batch lands on main as one PR with a merge commit, so every sub-PR's squash stays bisectable on main. Under the maintainer's later ruling, it lands only after the full ready-candidate proof, under the integration lease.

Proof

On b741ae0ad, with a private TMPDIR:

bun install --frozen-lockfile        # clean
bun run typecheck                    # clean
bun run build                        # clean
bun run lint                         # all gates clean
bun run check:pr --base origin/main  # Local preflight passed: 1180 pass, 0 fail

• Refreshed after ci: main red at b7b087d3bab4: browser #3511 cleared: merge commit 32c005e7f brings origin/main (bb91defdc) into the epic without conflicts. On it: install, typecheck, build and lint clean, and check:pr 1181 pass, 0 fail. The receipt below is from that run.
• Refreshed onto main 9805f52fd: merge commit b54027b5c. One conflict, in scripts/sync-project.ts: both sides added an epic to the "Answer quality" track, this one Epic: attach any file and route its contents through available capabilities #3150 and main Epic: external compute runs through interchangeable sandbox providers #3103. The resolution keeps both. On the merge: install, typecheck, build and lint clean, and check:pr 1196 pass, 0 fail. The receipt below is from that run.

check:pr receipt

{"version":1,"kind":"brain-check-pr-receipt","head":"7e1a23ef87c55e30215080ea57bce442a077cd2e","base":"origin/main","mode":"focused","startedAt":"2026-11-04T03:38:31.732Z","finishedAt":"2026-11-04T03:40:13.397Z","checks":[{"name":"all lint and leakage gates","categories":["changeset"],"outcome":"passed","elapsedMs":10890.156235},{"name":"environment documentation","categories":["changeset"],"outcome":"passed","elapsedMs":129.10731400000077},{"name":"pending changeset package names","categories":["changeset"],"outcome":"passed","elapsedMs":111.09675699999934},{"name":"contribution changeset","categories":["changeset"],"outcome":"passed","elapsedMs":20.813367999999173},{"name":"affected fast invariants","categories":["verify","unit"],"outcome":"passed","elapsedMs":90492.828612}]}

Checklist

• Focused local preflight receipt passed. The selected hosted proof runs under the lease before merge.
• Acceptance criteria from ui-server: design generic attachment intake, routing and content access #3151 are met in docs(plans): design generic chat attachment intake, ownership and on-demand reading #3301.
• The PR and ui-server: design generic attachment intake, routing and content access #3151 carry milestone 0.45.0.
• A changeset is included, or this changes nothing a consumer can see. (Docs only.)
• No personal data anywhere in the diff.
• The integration contract is unchanged.
• Docs under docs/ reflect the change.
• Provider history stays append-only. (Nothing on a turn's path changed.)

Anything left open

Open sub-PR #3342 (generic chat file admission) is not part of this batch.

🤖 Generated with Claude Code

[schlessera]

Landed as merge commit 0760f7832f3d81f897f7925b417e2a53dd2465b8. Its parents are main 54e47ae55 and head 7e1a23ef8, and its tree 7e22de832 equals the tested head tree. The final refresh, 7e1a23ef8, merged main 54e47ae55 into the epic without conflicts, picking up #3517 and #3533. check:pr passed on it (1196 pass, 0 fail), and the receipt is in the body. The full ready-candidate proof ran under the integration lease: CI run 41768602996 passed all 17 selected jobs, with none skipped or cancelled. epic/3150-attachments is fast-forwarded to the merge commit. #3151 is closed on 0.45.0, and epic #3150 stays open.