fix(tangent): give the project page columns that scale both ways

[camielvs]

Problem

The three columns were sized the wrong way round. The workarea had a fixed
width capped at 960, and the chat column took flex-1 — whatever was left:

[ dock 320 ][ chat: flex-1 ][ workarea: fixed 320–960 ]

On a wide screen chat swallowed every extra pixel — about 1270px of it on a
2560 display — while the workarea sat stuck at its cap, which is backwards for
the column that holds a pipeline graph. On a narrow screen there was nothing
left to take: 320 + 960 already exceeds a 1280 viewport, so with shrink-0 on
the workarea and min-w-0 on chat, the chat column was squeezed to zero and
disappeared.

What changed

The roles are swapped. Chat is the fixed column with a floor; the workarea takes
the remainder and grows:

[ dock ][ chat: 480, clamped 380–760 ][ workarea: flex-1, min 420 ]

• Chat starts smaller and cannot vanish. 480 by default, never below 380 at
  any window size. The drag handle moves to the chat column's right edge, which
  is the same boundary as before — it now drives chat's width rather than the
  workarea's.
• The workarea grows instead of capping, so a pipeline or run view gets the
  room on a large display.
• Below the width where all three can hold their minimum (dock 220 + chat
  380 + workarea 420 = 1020), the left dock gives up its width and shows its
  icon rail.

The auto-collapse only undoes a collapse it performed itself. Someone who closed
the dock and then widened the window meant to keep it closed, and reopening it
under them would read as the app fighting the mouse.

Rail icons

A rail is only as useful as its icons, and two were not pulling their weight
once the titles were hidden:

	before	after
Resources	Folder — identical to Project	FileText
Runs	Play — reads as "start something"	ListChecks

All six are now distinct: Project Folder, Sessions MessagesSquare, Agents
Bot, Assets Files, Resources FileText, Runs ListChecks.

Beta flags

Tangent Shell moves next to Projects — one is where the other is used — and
becomes just Tangent. Its description named the workspace concept, which the
UI does not otherwise expose:

Enable the Tangent Shell workspace: a projects area where you collaborate
with Tangent on…
Collaborate with Tangent inside a project on building, improving, and
debugging ML pipelines.

Testing

• New useNarrowLayoutDock.test.tsx (4), covering the "leave a dock the user
  collapsed alone" rule.
• pnpm run validate clean; npx vitest run 322 files / 3260 tests green.
• Column behaviour across window sizes, and the rail icons, were checked in the
  browser by the reviewer, not by me — jsdom has no layout, so the unit tests
  cover the collapse logic only.

🤖 Generated with Claude Code

[github-actions]

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A preview build has been created at: 09-23-fix_give_the_tangent_page_columns_that_scale/c03d155

[camielvs]

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Learn more

• fix(tangent): give the project page columns that scale both ways #2798 👈 (View in Graphite)
• fix(runs): say why the backend refused a run instead of that it did #2794 : 1 other dependent PR (#2796 )
• feat(tangent): brief the agent on naming, and on the project its runs belong to #2792
• feat(projects): fix cancelling, track shared projects, flag unreachable pipelines #2790
• feat(tangent): keep an agent's edits in frame on the canvas #2789
• feat(tangent): bring Tangent onto the dashboard #2787
• feat(tangent): show a project's runs on the tangent page #2786
• fix(projects): show an agent's run on the project it belongs to #2785
• fix(agent): submit a spec that came from the editor's store #2784
• chore: increase max turns in remote agent #2779
• fix(tangent): stop the tab strips scrolling up and down #2777
• feat(projects): make the agents' instructions a project document #2776
• feat(tangent): list the pipelines the backend holds #2775
• feat(projects): show a project's documents on both pages #2774
• fix(tangent): project window parity — share, new-session links, agent-created pipelines, and a folded-away project window #2773
• refactor(projects): describe a project's resources one way #2765
• feat(projects): delete and share a project from either page #2764
• feat: open a new project ready to work in #2763
• feat: let the project page and Tangent reach each other #2762
• fix: keep a long project name inside the tile it belongs to #2761
• feat: say so when Tangent cannot be reached #2760
• feat: open a project where the work happens #2759
• feat: run a pipeline inside a project #2754
• feat: add pipelines held in this browser to a project #2745
• feat: project page #2738
• feat: create a project from a tile in the grid #2735 : 2 other dependent PRs (#2736 , #2737 )
• feat: projects dashboard #2734
• chore: tangent - annotate runs submission to projectid #2758
• fix: tangent - proper debug sequence system prompt #2757
• fix: tangent - quick run button from mini content window #2744
• fix: tangent - remote agent send delta immediately #2743
• fix: tangent - mint proper authorization with tangent #2742
• feat: tangent - debug in tangent sequence #2741
• chore: add autolayout tool #2740
• feat: tangent - resource management via document entity #2733
• feat: tangent - interactive chips in tangent chat #2732
• chore: save id stack to replay ids on reloads #2731
• refactor: tangent - migrate tangetproectcontext onto mobx #2730
• feat: tangent - keep track of open tabs while switching sessions inside project #2729
• feat: tangent - remote agent for runview and editor #2728
• refactor: tangent - structured workarea target #2727
• feat: tangent - embedded pipeline run view #2726
• feat: tangent - embedded pipeline editor #2725
• feat: tangent - dynamic workarea remote tools #2724
• feat: tangent - resources management in project view #2723
• feat: tangent project view page #2722
• feat: workspaces and projects service #2720
• chore: api client for workspaces and projects #2719
• master

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