fix(local-model): say what is true of the Mac, and why a model is missing

Review fixes for the read-only recommendation and its card.

Recommendation (pure):
- `limited` is now a statement about the Mac: no model with 12 billion
  parameters or more fits. It is judged on everything that fits, before
  the disk filter and whatever the pick is. A 32 or 36 GB Mac whose pick
  is a 9B model no longer reads "This Mac can run a small model" above a
  list of 20B, 27B and 35B models, and knowing the chip no longer lowers
  the verdict. A small pick under `ok` carries a note that says so.
- A model that fits the memory but has no room on the disk is no longer
  dropped in silence: the best-ranked one is named in a note with the GB
  that are missing. A full disk cannot turn a 48 GB Mac into a
  small-model Mac.
- "Models fit, but not at a context a harness needs" has its own
  sentence with the budget and the need, worded as an estimate. The
  16 GB Mac mini misses by 1.3 points (10.3 of 10.4 GB) and was told
  flatly that its memory is too little, the sentence of an 8 GB Mac.
- The installed memory is named by the size the Mac is sold as (48, not
  51.5): the hardware line and the memory sentence. Every computed size
  stays decimal GB from the one formatter. An unknown memory size is no
  longer reported as "0.0 GB".
- Slow is graded on the unrounded speed: 9.95 to 9.9996 tokens per
  second printed as 10 and read ok.
- The disk sentence names the 10 GiB that must stay free, so its
  numbers add up for the reader.

Card and Settings group:
- The Settings group "Model on this Mac" is hidden on a server that is
  not a Mac, and until the first answer says it is one.
- Only `403 FORBIDDEN` is a refusal. `403 PASSWORD_CHANGE_REQUIRED`
  (an admin who must change the password) is a failed request and is
  asked again, so that admin no longer loses the card until a reload.
- Each fit and speed label carries what it measures as its tooltip and
  accessible name, an alternative with a speed estimate prints it, and
  the count beside "Other models that fit" is gone (it was the number
  of rows, capped at four, not the number of models that fit).
- The line saying nothing can be set up yet sits right under the pick,
  in the colour of every other line (it was 3.9:1), and says whose step
  it is.
- The dismissal key is named for this stage, so hiding the read-only
  card does not hide the install offer later.

Co-Authored-By: Claude Fable 5.1 <noreply@anthropic.com>

src/types/local-model.ts

@@ -15,10 +15,12 @@
  *
  * Three rules every producer and consumer follows:
  *
- * 1. ONE unit for a size a person reads: decimal GB, computed from bytes by `formatGb()` in
- *    src/local-model/format.ts. Every such size travels twice, as bytes (`needBytes`) and as the
- *    text to show (`needGb`, a number without the unit, such as '25.5'). The browser prints the
- *    text and never divides bytes itself. GiB appears only inside the budget math.
+ * 1. ONE unit for a computed size a person reads: decimal GB, computed from bytes by
+ *    `formatGb()` in src/local-model/format.ts. Every such size travels twice, as bytes
+ *    (`needBytes`) and as the text to show (`needGb`, a number without the unit, such as
+ *    '25.5'). The browser prints the text and never divides bytes itself. GiB appears only
+ *    inside the budget math. The one exception is the NAME of the installed memory: the card
+ *    says `HardwareFacts.memClassGb` (48 for a Mac sold with 48 GB), see that field.
  * 2. Every sentence or label the SERVER chooses comes from `LOCAL_MODEL_LABELS` below, so the
  *    browser can translate it (`codemanT(text, vars)`) and its i18n test can list every string.
  *    Numbers are never spliced into a sentence here: they travel in `vars` and fill the
@@ -33,7 +35,8 @@
  * How `HardwareFacts` was obtained.
  *  - `sysctl`: the spawn answered and `hw.memsize` parsed.
  *  - `os-fallback`: on macOS, but the spawn failed or timed out; memory, architecture and the chip
- *    string come from `node:os`, the rest is absent.
+ *    string come from `node:os` and the free disk from `statfs`. What only sysctl knows (`arm64`,
+ *    `translated`, `model`, `macosVersion`, `macosMajor`, `wiredLimitMb`) is absent.
  *  - `not-probed`: not macOS, so `sysctl` was never spawned.
  */
 export type HardwareProbeSource = 'sysctl' | 'os-fallback' | 'not-probed';
@@ -54,9 +57,19 @@ export interface HardwareFacts {
   translated?: boolean;
   /** Installed memory in bytes (`hw.memsize`, else `os.totalmem()`). The ONLY memory input of the budget math. */
   memBytes: number;
-  /** `memBytes` as a person reads it: decimal GB from `formatGb()`, without the unit ('17.2' for a Mac sold as 16 GB). */
+  /**
+   * `memBytes` in the unit of every computed size: decimal GB from `formatGb()`, without the unit
+   * ('17.2' for a Mac sold as 16 GB). NOT what the card calls the installed memory: that is
+   * `memClassGb`, see there.
+   */
   memGb: string;
-  /** The memory size the Mac is sold as: whole binary gigabytes (16, 32, 48). Tier rules and `TestedOn.memGb` use it. */
+  /**
+   * The memory size the Mac is sold as: whole binary gigabytes (16, 32, 48), 0 when the size is
+   * unknown. Tier rules and `TestedOn.memGb` use it, and it is the ONE size a person reads that
+   * is not decimal GB: the hardware line and the `memory` slot of `noneMemory` print it, because
+   * it is the number on the box and in About This Mac ("48 GB"), and '51.5 GB memory' reads as a
+   * different machine. Every computed size (need, budget, download, free disk) stays decimal GB.
+   */
   memClassGb: number;
   /** `machdep.cpu.brand_string` ('Apple M4 Pro'), else `os.cpus()[0].model`. */
   chip?: string;
@@ -97,7 +110,7 @@ export interface LocalModelEntry {
   label: string;
   /** SPDX id of the license ('Apache-2.0'). */
   license: string;
-  /** Parameter count in billions. Under 12 the verdict is `limited`, never `ok`. */
+  /** Parameter count in billions. When no model that fits has 12 or more, the verdict is `limited`, never `ok`. */
   paramsB: number;
   /** Size of the weights in bytes: both the download and what they take in memory. */
   bytes: number;
@@ -200,7 +213,10 @@ export type SpeedGrade = 'ok' | 'slow' | 'unknown';
  * Why the verdict is `none`.
  *  - `not-macos`: the server does not run on macOS (the card is hidden).
  *  - `intel`: a Mac without Apple silicon.
- *  - `memory`: no model fits the memory budget with any harness.
+ *  - `memory`: no model fits the memory budget at a context a usable harness needs. Three
+ *    headlines share this reason: `noneMemory` (nothing fits at any context), `noneMemoryContext`
+ *    (a model fits, but only below the context a harness needs: the sentence carries the budget
+ *    and the need) and `noneMemoryUnknown` (the memory size could not be read).
  *  - `disk`: models fit the memory, but for every one of them free disk minus the download is below 10 GiB.
  *  - `macos`: macOS is older than `LocalModelCatalog.minMacosMajor`.
  *  - `no-harness`: no catalogue harness is installed or installable and accepts a model.
@@ -228,12 +244,17 @@ export interface DeviceBudget {
  * `{placeholder}` slots are filled by the browser from `LocalModelMessage.vars`. `{name}` is
  * taken (the translator fills it with the display name), so no slot here is called `name`.
  *
- * | Key           | Slots (all text; sizes are decimal GB without the unit)                         |
- * |---------------|---------------------------------------------------------------------------------|
- * | `noneMemory`  | `memory`: `HardwareFacts.memGb`                                                 |
- * | `noneDisk`    | `download`: smallest download among the models that fit the memory; `free`:     |
- * |               | `HardwareFacts.freeDiskGb`; `missing`: download + 10 GiB - free                 |
- * | `noneMacos`   | `version`: `HardwareFacts.macosVersion`; `minimum`: the catalogue's minimum     |
+ * | Key                 | Slots (all text; sizes are decimal GB without the unit)                   |
+ * |---------------------|---------------------------------------------------------------------------|
+ * | `noteDiskDropped`   | `model`: label of the best model left out for disk space; `missing`: its  |
+ * |                     | download + the disk reserve - free                                        |
+ * | `noneMemory`        | `memory`: `HardwareFacts.memClassGb`, the size the Mac is sold as         |
+ * | `noneMemoryContext` | `budget`: `Recommendation.budgetGb`; `need`: the smallest need of any     |
+ * |                     | model at a context a usable harness works at                              |
+ * | `noneDisk`          | `download`: smallest download among the models that fit the memory;       |
+ * |                     | `reserve`: what must stay free after it (10 GiB, as decimal GB); `free`:  |
+ * |                     | `HardwareFacts.freeDiskGb`; `missing`: download + reserve - free          |
+ * | `noneMacos`         | `version`: `HardwareFacts.macosVersion`; `minimum`: the catalogue minimum |
  *
  * The word "Recommended" exists only in `headlineTested`, which may be used only when the
  * pick's `tested` is true. No catalogue row has a tested entry today, so it is never sent.
@@ -243,21 +264,33 @@ export const LOCAL_MODEL_LABELS = {
   headlineOk: 'Best fit for this Mac',
   /** Verdict `ok`, pick tested by us on a Mac like this one. */
   headlineTested: 'Recommended for this Mac',
-  /** Verdict `limited`. */
+  /** Verdict `limited`: no model with 12 billion parameters or more fits this Mac. */
   headlineLimited:
     'This Mac can run a small model. It handles small edits and questions. It does not replace a cloud model.',
   /** A note under an `ok` or `limited` pick whose `tested` is false. */
   noteUntested: 'Not yet tested by us on a Mac like this.',
+  /** A note under an `ok` pick that is itself a small model: larger ones fit this Mac, but rank lower or have no room on the disk. */
+  noteSmallPick:
+    'The best fit is a small model. It handles small edits and questions. It does not replace a cloud model.',
+  /** A note when a model that fits the memory was left out because its download would not leave the disk reserve. */
+  noteDiskDropped:
+    '{model} fits the memory of this Mac too, but its download needs about {missing} GB more free disk space.',
   fitGood: 'Good',
   fitTight: 'Tight',
   speedSlow: 'Slow',
   speedUnknown: 'Speed unknown',
   noneNotMacos: 'Codeman recommends a local model only on a Mac with Apple silicon.',
   noneIntel: 'This Mac has an Intel processor. Local coding models need Apple silicon.',
+  /** Reason `memory`: nothing fits at any context. */
   noneMemory:
     'This Mac has {memory} GB of memory. That is too little to run a model that can drive a coding agent, so Codeman recommends none here.',
+  /** Reason `memory`: a model fits, but only below the context a harness needs. Says both numbers, and that they are an estimate. */
+  noneMemoryContext:
+    'Codeman estimates that this Mac can give a model about {budget} GB of memory. The smallest model a coding agent can work with needs about {need} GB. That leaves no safe margin, so Codeman recommends none here.',
+  /** Reason `memory`: the memory size could not be read, so no size is stated. */
+  noneMemoryUnknown: 'Codeman could not read how much memory this Mac has, so it recommends no model here.',
   noneDisk:
-    'Not enough free disk space. The smallest model that fits this Mac is a {download} GB download and {free} GB is free. Free up about {missing} GB.',
+    'Not enough free disk space. The smallest model that fits this Mac is a {download} GB download, and {reserve} GB must stay free after it. {free} GB is free now. Free up about {missing} GB.',
   noneMacos: 'This Mac runs macOS {version}. Local models need macOS {minimum} or newer.',
   noneNoHarness: 'No coding agent that Codeman can connect to a local model is available on this Mac.',
 } as const;
@@ -265,7 +298,7 @@ export const LOCAL_MODEL_LABELS = {
 /** One of the texts in `LOCAL_MODEL_LABELS`. The payload's label fields are typed with it, so an off-list string does not compile. */
 export type LocalModelLabel = (typeof LOCAL_MODEL_LABELS)[keyof typeof LOCAL_MODEL_LABELS];
 
-/** The headline of each `none` reason. */
+/** The headline of each `none` reason. `memory` has two more (`noneMemoryContext`, `noneMemoryUnknown`), see `NoneReason`. */
 export const LOCAL_MODEL_NONE_LABELS: Record<NoneReason, LocalModelLabel> = {
   'not-macos': LOCAL_MODEL_LABELS.noneNotMacos,
   intel: LOCAL_MODEL_LABELS.noneIntel,
@@ -317,7 +350,7 @@ export interface Candidate {
   speed: SpeedGrade;
   /** `speedSlow` or `speedUnknown`. Absent when `speed` is `ok`. */
   speedLabel?: LocalModelLabel;
-  /** Estimated generation speed. Present exactly when `speed` is not `unknown`. */
+  /** Estimated generation speed, rounded to one decimal. Present exactly when `speed` is not `unknown`. `speed` is decided on the unrounded figure. */
   tokensPerSecond?: number;
   /** A `TestedOn` entry of the model matches this Mac (same chip, same `memClassGb`) and this harness. */
   tested: boolean;
@@ -325,22 +358,25 @@ export interface Candidate {
 
 /**
  * The answer of `recommend()`.
- *  - `ok`: `pick` is the best candidate and its model has at least 12 billion parameters.
- *  - `limited`: `pick` is the best candidate, but its model has fewer than 12 billion parameters.
- *    The card says so and never says "Recommended".
+ *  - `ok`: `pick` is the best candidate, and at least one model with 12 billion parameters or
+ *    more fits this Mac's memory at a context a usable harness works at. The pick itself can be
+ *    smaller (a larger model may fit only tightly, have no speed figure, or have no room on the
+ *    disk): `notes` then carries `noteSmallPick`.
+ *  - `limited`: `pick` is the best candidate, and NO model with 12 billion parameters or more
+ *    fits. The card says so and never says "Recommended".
  *  - `none`: no pick; `reason` says why.
  */
 export interface Recommendation {
   verdict: 'ok' | 'limited' | 'none';
   /** Present exactly when `verdict` is `none`. */
   reason?: NoneReason;
-  /** What the card says first: `headlineOk`, `headlineTested`, `headlineLimited` or the `none` reason's sentence. */
+  /** What the card says first: `headlineOk`, `headlineTested`, `headlineLimited` or a `none` sentence. */
   headline: LocalModelMessage;
-  /** Further sentences under the headline (`noteUntested` today). May be empty. */
+  /** Further sentences under the pick, in this order: `noteSmallPick`, `noteDiskDropped`, `noteUntested`. May be empty. */
   notes: LocalModelMessage[];
   /** Present exactly when `verdict` is `ok` or `limited`. */
   pick?: Candidate;
-  /** The next models that fit (at most four, each at its best context and harness), best first. Empty when `verdict` is `none`. */
+  /** The next models that fit and have room on the disk (at most four, each at its best context and harness), best first. Empty when `verdict` is `none`. */
   alternatives: Candidate[];
   /** `DeviceBudget.budgetBytes`. 0 when no budget is computed: not macOS, or a Mac without Apple silicon. */
   budgetBytes: number;