dsh-t3-new-session-screen

T3 Code's New Session screen for the DeepSeek Harness composer.

Three things that screen has and DeepSeek Harness's blank session does not:

• What should we build in <project>? — the headline from T3's DraftHeroHeadline, where the project name is itself the picker.
• A reasoning-effort picker — T3's TraitsPicker, surfaced in the composer tool row instead of hidden behind the model menu.
• A git branch picker — T3's BranchToolbar, with real git checkout.

Credit

The screen this plugin implements is T3 Code's. The headline sentence and its inline project control, the effort picker's shape, and the branch strip with its searchable ref menu are all theirs. T3 Code is open source under MIT; this port keeps the same behaviour and swaps the data underneath for DeepSeek Harness's own services. Please support the original project.

Features

• The headline. What should we build in <project>?, centred over the composer, with the project name underlined and clickable. Clicking it opens a T3-shaped project menu: every registered workspace, a check on the current one, a divider, and New project. Picking a project moves the blank session to it. DSH renders its own headline from a literal string with no slot, so this plugin fills the only additive hole in that row (conversation.hero.brand.mark) and suppresses the shipped title beside it. The template is configurable, and {project} marks where the control goes. Until a project is chosen the sentence is not run at all: the headline is the call to action alone — Choose a project to start — as T3's is, so the empty state never claims a project that does not exist yet. DSH's own workspace chip shares the row below the headline with the agent-preset seat; with the headline carrying the project, that chip leaves the layout too, and the preset seat it used to lead re-seats on the composer's right edge — see Alignment.
• Reasoning effort. A gauge control in the composer tool row showing the level the current model is actually using (Off, Low, High, Max for DeepSeek's own models). The menu carries each level's description and a check on the current one. It reads and writes the same per-session model directory the model seat uses, so the model seat's own label updates with it. A model that advertises no effort levels renders no control at all — effort is a per-model capability, not a global preference.
• Git branch. A strip under the composer card: the checkout on the left, the current ref on the right. The ref menu searches, lists local and remote refs, labels current / default / remote, and switches with git checkout <ref>. A Create new ref row appears once the query names a ref that does not exist yet, and runs git checkout -b. DSH ships no git surface of any kind, so every fact here comes from this bundle's Host half. The strip is aligned on the composer's shared width axis, not on the card — see Alignment.

Screenshots

The New Session screen	Project menu	Branch picker	Reasoning effort

Install

From this repository:

dsh plugin --profile web add github:yusufameri/dsh-t3-new-session-screen

Once the package is on npm, the registry form is one word shorter:

dsh plugin --profile web add dsh-t3-new-session-screen

Either reconciles the profile's bundle list, so the next boot merges the plugin's patch and loads its client half. Removing the bundle restores the shipped headline, model seat and composer with no residue.

Configuration

Every field is optional; the defaults render the whole screen. Set them on the bundle's row in the profile's cordis.patch.yml:

- id: t3-new-session-screen
  name: 'dsh-t3-new-session-screen'
  config:
    headlineText: 'What should we build in {project}?'
    effortSlot: right
    branchCreateEnabled: false

Key	Default	Meaning
headlineEnabled	true	Replace the blank-session headline with the T3 sentence.
headlineText	What should we build in {project}?	Headline template; {project} becomes the interactive project name. Without the hole the sentence renders as plain text; with no project chosen it gives way to the call to action.
hideShippedHeadline	true	Hide DSH's own "Into the Unknown" title beside the headline.
hideWorkspaceChip	true	Hide the shipped workspace chip under the headline, which the headline supersedes.
effortEnabled	true	Reasoning-effort picker in the composer tool row.
effortSlot	left	Which composer seat the effort picker occupies: left (beside the permission and plan controls) or right (beside the model seat).
branchEnabled	true	Git branch strip under the composer, on the new-session screen and in an active session.
branchCreateEnabled	true	Offer Create new ref (git checkout -b) in the branch picker.
gitEnabled	true	The git bridge behind the branch strip. Turning it off leaves the strip absent.
gitTimeoutMs	30000	Budget of one git child process.

The client half reads the resolved configuration from the Host over the same route the branch data uses, so a change takes effect on the next page load.

How it works

The whole screen is contributed through DSH's own seams.

Piece	Seam
Headline	conversation.hero.brand.mark (single, root) — the only additive hole in DSH's headline row.
Project menu	conversation.hero.workspace (single, root) at priority -1, which shadows the shipped WorkspacePicker in the same cell.
Project roster	The root useWorkspaces standard hook, fed by ctx.slots.provideRoot.
New project	ctx.uiWorkspace.pickDirectory() then ctx.workspaces.create({ path }).
Reasoning effort	conversation.input.left / .right (list), reading ctx.modelDirectories.directoryFor(sessionId).
Branch strip	conversation.input.dock (one seat for both phases).
Hero workspace row	No seat of its own. The shipped row is re-declared: its workspace chip leaves the layout and its agent-preset seat is trailed onto the composer axis, keyed off a data-t3nss-preset-trailing attribute the plugin sets on <html>.
Working directory	ctx.sessions.list.getSnapshot().byId[sessionId]?.cwd.
Git	The Host half's fenced POST /t3-new-session/api route (config, git.status, git.branches, git.checkout, git.createBranch), running git through node:child_process.

Two details are load-bearing rather than incidental:

• The client half must inject remote and remote.session. modelDirectories.directoryFor resolves through Cordis's caller-context tracker, so a plugin that reads the model directory without holding the same remote namespace gets cannot get property "remote.session" without inject and the effort control silently disappears.
• The Host half imports nothing outside node:*. A plugin installed as a directory link resolves its imports from its own real path, where none of DSH's @deepseek-ai/* packages are reachable, so the configuration schema is a hand-written Standard Schema rather than a Schemastery one — Cordis needs nothing more than a synchronous ~standard.validate.

Alignment

The screen is measured against T3's own numbers rather than eyeballed. T3's composer shell is max-w-3xl with --chat-composer-drawer-inset: 1.375rem, and its context strip is inset by two of those (44px) with ps-1 pe-2. DSH's axis is --dsh-composer-side-clearance (16px), --dsh-composer-dock-inset (8px) and --dsh-composer-card-max-width, and the shipped QueueDock derives its width from the same three values. The strip uses that derivation, so with the shipped profile it lands on the card's content box:

Element	X range
Composer card	498..1375	877px
Composer tool row, content box	506..1367	861px
Headline stack (HeroShell)	506..1367	861px
Branch strip	506..1367	861px
Hero preset seat (right-aligned)	1218..1367	149px

All four of those boxes share centre 936, and the strip's text sits 4px under the card — which is exactly what T3's -mt-4 + pt-5 pair nets out to. Inside the tool row the reasoning-effort control is 28px tall and vertically centred with the attach button and the permission control (all 513..541).

The preset seat is the row's only label-sized element, so only its right edge is a fixed number: the seat is content-sized (149px for Standard mode), and its left edge follows whatever DSH names the preset — which is why it is not in the centre group above. Its right edge lands on the same 1367 as the strip, the headline stack and the tool row's content box, which is also the send button's and the strip's trailing control's right edge — the row reads as one trailing column above the card rather than a chip mid-row.

Two details are load-bearing and easy to regress:

• box-sizing: border-box on the strip. Without it the horizontal padding adds to width: 100% and the strip overflows its stack by the padding on each side — which is what it did before this was measured.
• The width / max-width pair. On the hero the stack is already inset by one side clearance per edge, so both clearances and both dock insets come off the percentage. In an active session the stack is the full seat width and max-width does the clamping while margin-inline: auto re-centres it — the same 861px at the same 506px start, from a different parent.

The hero workspace row is the one place the plugin adjusts DSH's own box rather than filling a seat. Removing the shipped workspace chip from the row is what frees the preset seat, and it is the layout removal that matters: visibility: hidden — the obvious way to hide an element whose behaviour is still wanted — leaves its 226px box behind for this repository's own name, and the seat beside it then sits at whatever x that box ends on. Two things follow, and both are what the check below measures:

• the chip is display: noned, not hidden, so nothing it used to size survives in the row;
• the seat is trailed with an auto left margin plus an 8px right margin, not with justify-content on the row: the row belongs to DSH, the margins belong to the seat, and an auto margin keeps the slip right at any row width — the row's own right padding (16px) is one side clearance, so the 8px margin is what lands the seat on the axis rather than on the card's outer edge.

scripts/measure-alignment.mjs re-checks every number above against a running page and exits non-zero on a regression — including checks 6 and 7, which fail on either half of that mistake: a seat that stops ending on 1367, and a chip that starts occupying space again.

Differences from T3

DSH has no equivalent of these T3 concepts, so the port leaves them out rather than faking them:

• No local/worktree environment switch. T3's strip opens with a Current checkout / New worktree selector. DSH has no worktree concept, so the strip's left label reports the checkout and is not a menu.
• No pull-request badge on the strip.
• The strip is ordered below the card rather than laid out there. DSH's blank-session hero renders no extension seat below the input card, so the strip is contributed to the seat above it and moved down with order. Every wrapper the renderer puts around a slot occupant is a contents-only box, so the strip is a flex item of the composer stack and the ordering works without touching shipped CSS. In an active session DSH's own context meter occupies the space directly under the card, so the strip sits below that instead.

One behaviour worth knowing: DSH's session/selectModel writes the session selection and the deployment default, so picking an effort level also makes it the default for new sessions. That is the Host's behaviour, not this plugin's; it is the same thing the shipped model menu does.

Development

# one-time: shim pnpm if it is not on PATH
mkdir -p ~/.dsh/dsh-runtimes/shim

# install into a scratch profile and boot it
dsh plugin --profile t3demo add "$PWD"
dsh --profile t3demo --port 8899 --no-open

The capture tooling behind assets/ is in scripts/: record.mjs drives a scripted interaction over one Chrome DevTools Protocol connection (and can record frames), encode-gif.py turns those frames into the GIF, and capture-stills.json / demo-steps.json are the two scripts it runs.

CDP_PORT=9333 node scripts/record.mjs scripts/capture-stills.json --no-frames
CDP_PORT=9333 node scripts/record.mjs scripts/demo-steps.json /tmp/frames
python3 scripts/encode-gif.py /tmp/frames assets/demo.gif

scripts/measure-alignment.mjs is the alignment check described in Alignment. Point it at a page running this plugin and it fails with a non-zero exit if any of those numbers move:

CDP_PORT=9333 node scripts/measure-alignment.mjs

License

MIT. T3 Code is MIT too; see Credit.