192 lines
10 KiB
Markdown
192 lines
10 KiB
Markdown
# The Arsenal develop economy, and what the save's blob indexes
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**2026-08-11.** The save file's 54-byte blob was shown to be per-item development
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state by [a runtime differential](structures/savegame-format.md#the-develop-differential-one-weapon-three-fields) —
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one weapon bought, two entries moved, `2 → 4` for the item and `0 → 2` for the
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successor. That named the *values*. This note names the *index space*, and in
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passing recovers the whole develop economy from the disc.
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## Where the Arsenal gets its data
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`dat/GP_HANGAR_ARSENAL.pak` carries one screen-config record per language whose
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fields point at the rest:
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```
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PATH = dat\GP_HANGAR_ARSENAL.pak+eng\
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WEAPON = weapon.tbl STRINGS = strings.tbl
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WEAPON_CATEGORIES = 8 Detail_Window_Known / Detail_Window_Unknown
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ConditionToDevelop = 757,228 WeaponDesc = 734,502 Range = 891,73 …
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```
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`WEAPON_CATEGORIES = 8` is the eight tabs the screen cycles with LB/RB (GUN,
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BEAM, LASER, MULTIPURPOSE MISSILE, ANTI-SHIP MISSILE, BOMB/ROCKET, CANNON,
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SPECIAL). The `…= x,y` fields are screen positions for that screen's labels —
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`ConditionToDevelop` is *where the conditions text is drawn*, not a condition.
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### `eng\weapon.tbl` — the item table (IDXD, schema `0x03c244b5`, 66 records)
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Its string pool opens with a stage list, then the literal key `WEAPONS`
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followed by the item ids **in table order**:
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```
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No_Equipment, Machiene_Cannon_MG1, Machiene_Cannon_MG2H, Machiene_Cannon_MG3,
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Machiene_Cannon_MG5H, Broad_Sword_SG1, Swing_Sword_SG2H, Twin_Sword_SG3II,
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Frail_GP37, Stiletto_BG1, Dagger_BG2, Rapier_BG4H, Pilum_BP, … , Wep_83,
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Wep_84, Wep_85, NullWeapon_Arm1, NullWeapon_Arm2, NullWeapon_Arm3
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```
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The ids are grouped by the eight categories in the same order the screen shows
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them, which is why `No_Equipment … Wep_83` is exactly **54** entries — the blob's
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length.
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Each item then has a record: `Size, Weight, Range, Power, Speed, Stage,
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MissionObjective, Dependency, Points`. For the **first** record all of it reads
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straight out, and it matches the running game exactly:
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| field | disc | in-game DATA SHEET for Light Machine Gun MG I |
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|---|---|---|
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| Range | `D` | `Range Class D` |
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| Power | `E` | `Damage Class E` |
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| Speed | `-` | `Speed Class –` |
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| Weight | `0.3` | `Weight Class Light` |
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| Points | `4000` | `4000 P` on the develop row |
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**Caveat, and it is a real one:** IDXD string pools store each distinct string
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*once*, so from the second record onward every value that repeats an earlier
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string is absent from the token stream. Record 2 (MG2H) shows only its unique
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values — `0.4` and `3000` — and record 6 shows no number at all because its cost
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had already been seen. So `weapon.tbl`'s per-item fields cannot be read from the
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pool alone; they need the binary node/index region, which is still undecoded
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(see the module docs in `idxd.rs`). The prose table below is the practical
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substitute.
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### `eng\strings.tbl` — the economy in prose (IXUD, UTF-16BE)
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The same pak's string table holds, per item: the internal id, the display name,
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the description, and a **"Conditions to obtain …"** block that spells out the
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gate and the price:
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> Conditions to obtain Light Swivel Machine Gun MG2H — Completed development of
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> the Light Machine Gun MG1 — Must spend 3000 points to develop
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All 60 of them are extracted to
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[`captures/arsenal-develop-conditions.csv`](captures/arsenal-develop-conditions.csv)
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with the stage gate, the cost and the prerequisite split out. The shape of the
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economy:
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- gates are **stage completion** (`Complete Stage 1 … 15`), **a predecessor
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item** (`Completed development of the …`), or **an ace kill** (`Shoot down the
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ace pilot in Stage 11/13/14`);
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- costs run 3 000 → 350 000 points, and **twenty items have no cost at all**
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(`Tomahawk Alpha Rail Gun — Complete Stage 1`). Those are still *bought*, for
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**0 P** — see the probe below, which caught one at `0 P` — which is why they
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read as `Developed` in a list the player never spent points in;
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- two items are anomalies worth flagging: `Adhesive Mine B2A` says "Must spend
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points to develop" with **no number**, and ten late entries (`Ballista GSH`,
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`Designator LH`, `Smoke Marker Launcher`, `Bumble UV`, `Ballista 24 Rocket
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Launcher`, `Thrush 220AM`, `Divider L3GP`, `Mace GP25H`, `Thor Gun System`,
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`Spitfire BX`) have a conditions *header* and no conditions — ❔ cut content or
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non-player weapons.
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## What the blob indexes: the first 32 entries, confirmed
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Predicting the save state from the conditions and comparing against the actual
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blob is a strong test, because it is made **before** looking at the blob. At the
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captured state (Stage 1 complete, Stage 02 at standby, 4101 P) the conditions say
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exactly six items are developable — Light Machine Gun MG1, Broad Sword SG1,
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Dagger BG2, Pilum BP, Hound SMH, Dart 23 Rocket — and the blob's **six** `2`s sit
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at WEAPONS-order indices **1, 5, 10, 12, 27, 31**, which are those six items, in
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order. Nothing had to be fitted.
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| blob | value | item (WEAPONS order) | confirmed by |
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|---|---|---|---|
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| 0 | 4 | `No_Equipment` | always available |
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| 1 | 2→4 | `Machiene_Cannon_MG1` | the differential: bought for 4000 P |
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| 2 | 0→2 | `Machiene_Cannon_MG2H` | the differential: announced as newly developable |
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| 5 | 2 | `Broad_Sword_SG1` | `BROAD SWORD SG1 5000P`, **below the fold** in the GUN list |
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| 9 | 4 | `Stiletto_BG1` | `Developed`; "Initially Mounted"; mounted as NOSE WEAPON |
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| 10 | 2 | `Dagger_BG2` | `DAGGER BG2 5000P` |
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| 12 | 2 | `Pilum_BP` | `PILUM BP 6000P` |
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| 21 | 4 | `Falcon_9AM` | `Developed`; "Initially Mounted"; mounted as MAIN WEAPON 1 |
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| 22 | 4 | `Buzzard_10AM` | `Developed`; free at Stage 1 |
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| 26 | 4 | `Terrier_SMH` | `Developed`; free at Stage 1 |
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| 27 | 2 | `Hound_SMH` | `HOUND SMH 10000P` |
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| 31 | 2 | `Dirt_23_Rocket` | `DART 23 ROCKET 3500P` ("Dart" is the localised "Dirt") |
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Twelve concordances, no contradiction, over indices 0–31.
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## What the blob does **not** index: the tail is unexplained
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Past index 31 the same alignment fails, and it fails against the screen, not
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against a theory:
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- `Tomahawk_a_Rail_Gun` is WEAPONS index **38** and the CANNON list shows it
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`Developed` (it is free once Stage 1 is complete) — but **blob[38] = 0**.
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- The blob's remaining `4`s are at **33, 39, 45, 46, 47**. In WEAPONS order those
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are `EMP_Mine_B8E`, `Sling_75KG`, `Shield_Doubler`, `Booster`,
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`FireControlSystem` — and **every one of them is shown as not developed**:
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BOMB/ROCKET lists only `DART 23 ROCKET 3500P`, CANNON only the Tomahawk, and
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**the SPECIAL tab is entirely empty** (all rows dashed). Their conditions agree
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— Shield Doubler needs Stage 12, Booster an ace kill in Stage 11, FCS Stage 6.
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So five `4`s in the tail correspond to nothing the Arsenal reports as owned, and
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one genuinely-owned item reads `0`. A single `+1` shift does not repair it
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either: `blob[39] = 4` would put the Tomahawk right, but then `blob[33] = 4`
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lands on `Arrow_27_Rocket` (Stage 2 + 5000 P, unreachable here) and 45/46/47
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still land on locked SPECIAL items.
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### Tested actively, with a hand-written save
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Waiting for a mission payout was not necessary. The save container's derived
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fields turned out to be reproducible (see
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[`savegame_edit.py`](../../tools/re-capture/savegame_edit.py) — the whole
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container re-wraps **byte-identically**), so the blob could be *written* and the
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result read off the screen. A probe save was built in our own throwaway slot 03
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with the blob zeroed except `0, 9, 21, 33, 38, 45 = 4` and `39, 46 = 2`, and it
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**loaded**.
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What it showed:
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- **The controls rendered.** `9` → BEAM shows `STILETTO BG1 Developed`; `21` →
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MULTIPURPOSE MISSILE shows `FALCON 9AM Developed`. So a hand-written `4` does
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reach the screen, and indices 9 and 21 are those items — now by experiment,
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not by correlation.
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- **The tail probes rendered nothing.** `33` should have made a BOMB/ROCKET row
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`Developed` (row 3 of that list, on screen, not below the fold) — it stayed
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dashed. `45` should have made a SPECIAL row `Developed` — the SPECIAL tab
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stayed entirely empty. And `38` should have been the Tomahawk — instead the
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CANNON list showed `TOMAHAWK ALPHA RAIL GUN — 0 P`, i.e. *not owned*.
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- **Clearing the real save's tail `4`s cost the Tomahawk its status.** In the
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unedited save the Tomahawk reads `Developed` while `blob[38] = 0`; the probe
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cleared `{22, 26, 39, 46, 47}` and the Tomahawk stopped being owned — so its
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flag is one of the cleared entries, with **39** the positional candidate. A
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uniform `+1` shift past index 32 would explain that, but it fails elsewhere:
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under it the real save's `45/46/47` are Chaff Flare Dispencer / Shield Doubler
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/ Booster, and the SPECIAL tab is empty in that same save.
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So the tail is not a shifted copy of the list either. **Status: ❔** — the value
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alphabet and indices 0–31 are settled; indices ≥32 are not, and must not go into
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the reimplementation. The next probe is cheap now that saves can be written: set
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one tail index at a time and read which row changes.
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### Two behaviours the probe exposed
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- **`2` is derived, not stored.** On load the title recomputes which items are
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developable from its own conditions and *announces the difference* — zeroing
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Light Machine Gun MG1 and Broad Sword SG1 produced "You can now develop Broad
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Sword …" and both came back priced in the list. Only the owned (`4`) entries
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are authoritative state; writing `2` is pointless, and writing `0` over an
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item whose conditions are met is undone at load.
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- **The free items are bought for zero, not granted.** `TOMAHAWK ALPHA RAIL GUN
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— 0 P` is what an unowned no-cost item looks like. That is the real reason a
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save where the player never spent points still shows items as `Developed`
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(this note previously said "granted" — the mechanism is a 0 P purchase).
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## Evidence
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- [`captures/arsenal-develop-conditions.csv`](captures/arsenal-develop-conditions.csv) — all 60 conditions blocks.
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- [`captures/arsenal-categories-all.png`](captures/arsenal-categories-all.png) — the eight category tabs.
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- [`captures/arsenal-gun-below-fold.png`](captures/arsenal-gun-below-fold.png) — Broad Sword SG1, the entry that is not visible without scrolling.
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- [`captures/arsenal-probe-save-result.png`](captures/arsenal-probe-save-result.png) — the hand-written save's result: controls at 9/21 render `Developed`, the tail probes render nothing, and the Tomahawk shows `0 P`.
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- [`captures/arsenal-gun-list-predevelop.png`](captures/arsenal-gun-list-predevelop.png) · [`captures/arsenal-mg1-developed.png`](captures/arsenal-mg1-developed.png) — the differential itself.
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