Core rotation & Next Cast logic

• Guitar Hero–style single highway bar: SWP, VT, Mind Blast, and SWD each ride their own thin sub-lane on one shared bar, positioned by real "need time" (accounts for cast time, not just raw remaining duration).
• "Next Cast" readout shows the single best action to press right now, including Inner Focus, Trinket/Destruction Potion during lust, Dark Rune/Mana Pot/Shadowfiend at configurable mana thresholds, and Fade at a configurable threat threshold.
• Look-ahead collision protection: before recommending anything, the engine checks whether casting it would occupy you long enough that SWP or VT would cross its own deadline in the meantime — if so, the dot force-preempts the original pick, even before it hit its own "green" window. (Example: Mind Blast comes off cooldown while VT has 2s left — VT now correctly jumps the queue instead of falling off mid-MB-cast.)
• VT always wins over SWP in a collision tie — VT's party-wide mana return is worth more than SWP's personal damage.
• Mind Flay clip-awareness: tracks the live channel and only recommends clipping it right after a tick lands (not mid-tick), unless a genuine SWP/VT emergency justifies interrupting immediately. Starting Mind Flay is itself subject to the same collision check as everything else.
• Fade / threat management: recommends Fade once your live threat (via the game's own threat API) crosses a configurable percentage, gated to group/raid only. Treated as a real emergency — can interrupt Mind Flay mid-tick.
• Bar-Queue Colors: the 4 highway lane bars are colored by their rank in the cast order (1st/2nd/3rd/4th up), not just their own individual readiness — fully player-customizable colors.
• Latency-aware timing: the "safe to recast" window for SWP/VT is read live from the game's own connection latency instead of a guessed fixed buffer, since Shadow Priest spells are confirmed hitscan (no travel time).

Rotation & Tracking configuration

• Rotation tab: fully independent, reorderable, toggleable priority list covering Fade, Trinket, Destruction Pot, Inner Focus, Dark Rune, Mana Pot, Shadowfiend, VT, SWP, Mind Blast, SWD, and Mind Flay.
• Trinket/Destruction Pot: independent "While Lusted" / "Recommend when Exhausted" checkboxes (the latter checks the actual post-lust Exhaustion/Sated debuff, not just "lust isn't up").
• Dark Rune, Mana Pot, Shadowfiend, and Fade each get an inline editable trigger threshold (mana % or threat %) directly on their row.
• Per-item enable/disable checkboxes throughout, so unused items (no trinket that raid, no Destro Pot on hand, etc.) can be hidden from both the cooldown row and the recommendation logic.

Buff Watch

• Tracks Shadow Protection, Fortitude, Inner Fire, and Divine Spirit — shown only when actually missing, works in any spec (not gated by Shadowform), toggleable per-buff.
• Lives on its own independent, draggable frame with short acronym labels and a single "Missing" indicator instead of repeating it per icon.

UI & customization

• Split into three independently movable/lockable frames: Next Cast, Cooldowns, and Buff Watch — one shared lock toggle, each remembers its own position.
• Options panel split into General / Tracking / Rotation tabs, centered content throughout.
• Scale, Icon Size, and Bar Width controls; customizable Ready/Soon/Not-yet colors and Bar Queue colors.
• Load In Combat Only (hides Next Cast/Cooldowns outside combat; Buff Watch stays available) and Show Test Frames (forces visibility for repositioning).
• Shadowform gate: the rotation-specific frames disable themselves outside Shadow spec, live-updating on respec.

Bug fixes (client-specific API issues)

• Fixed several silent failures caused by APIs that don't exist on this client (GetItemInfoInstant, GetItemCooldown) — these were causing cooldown-row items to error out or, worse, silently report "always ready" regardless of actual cooldown state (the root cause behind potions/Dark Rune getting recommended while genuinely on cooldown).
• Fixed the Shadowform spec-gate not actually gating anything for non-Shadow specs — root cause traced to a spellbook-scanning check with a fail-open safety net masking the real failure.
• Fixed Mind Blast/SWD flickering unavailable during the GCD sweep.
• Every cooldown/tracking check now runs in its own isolated error boundary, so one broken lookup can't silently blank out unrelated parts of the UI.

Research-based corrections (mechanics verified, not assumed)

• Confirmed items (trinkets, potions, Dark Rune) don't trigger the shared GCD in this era of WoW, unlike spell casts — fixed the collision math that had been overstating how long using one would "block" other casts.
• Confirmed Mind Flay's tick count is haste-independent in TBC (haste only shortens the channel) — corrected an earlier assumption based on a source describing a much later expansion's mechanics.
• Confirmed Destruction Potion and Mana Potion share a cooldown category, while Dark Rune does not.
• Confirmed Fade's real numbers (330 mana, 10s duration, 30s cooldown at max rank) and its actual mechanic (temporary threat suppression, not permanent removal).

Since the last changelog (1.16.3 → 1.20.3)

New: Mind Flay's own highway lane

• A 5th lane, positioned between VT and MB. Unlike the other four, Mind Flay doesn't have a natural countdown - it's binary, so it behaves differently: idle in a customizable blue by default, switching to green the moment it's genuinely the resolved recommendation.
• A proportional fill bar (replacing an earlier discrete-tick-marks attempt that didn't read well in practice) shows how much of the 3-tick channel is actually worth taking before a clip is needed - 2/3 green means take 2 ticks then clip, full green means the whole channel is safe. Extended to compute even before the channel starts, so it's accurate the instant MF becomes the recommendation.
• Bold tick-boundary markers layered above the fill so they stay visible even when the bar is green, after an earlier attempt wasn't visible enough.
• Mind Flay's active/idle colors are fully independent from the general "Ready" note color - an earlier version reused that color directly, which meant a customized Ready color unexpectedly (and confusingly) applied to Mind Flay too.

New: Vampiric Embrace added to the rotation

• Previously only tracked as a standalone cooldown, never recommended. Confirmed via direct TBC spell data before implementing: 1 minute duration on a 10 second cooldown, 2% mana - that ratio makes "keep it up whenever possible" a reasonable default, unlike Trinket/Destro's burst-window timing.
• Gated to skull-marked targets only (reusing the same infrastructure built for Destruction Potion) - normal mobs and dungeon bosses die too fast for its healing-via-damage effect to be worth the GCD.

Next Cast icon overhaul

• Only shows cooldown-type items now (Fade, VE, Trinket, Destro, Dark Rune, Mana Pot, Shadowfiend, Inner Focus) - never a damage-rotation ability, since the highway bars already cover those. Shows blank when nothing but damage abilities are currently queued, instead of defaulting to one.
• Thicker border (4px vs the standard 2px) so it's easier to tell at a glance whether it's actually showing green through the flashing nag effect.
• Icon border color now matches its bar's Bar Queue Colors rank instead of showing its own separate readiness color - the two could previously disagree.
• "Green" is now strict everywhere: a highway bar only ever shows green if it's genuinely the overall top recommendation, never just "soonest among these 4 specifically." If the true top pick is a cooldown, no bar shows green - every rank shifts down a slot instead.

Critical bug fix: addon completely failing to load

• A tester's game showed /sh falling through to WoW's built-in /shout - meaning the addon's slash commands never registered at all, and nothing in the UI ever appeared.
• Root cause, confirmed via a live in-game BugSack error (not guessed): Lua 5.1's hard 60-upvalue-per-function limit. WoW's actual runtime enforces this; the Lua 5.4 compiler used for syntax-checking all session does not, which is why it passed every check right up until it was tested in-game. UpdateQueue() had grown, across many features added over time, to reference more than 60 outer-scope variables - Lua 5.1 refuses to even compile a function past that point.
• Fixed by extracting the two largest self-contained chunks of that function (Mind Flay lane logic, Bar Queue Colors ranking) into their own separate functions, each carrying its own variables independently.
• Verified directly against luac5.1 - installed specifically to test against the same compiler version WoW itself uses - rather than estimated. Both luac5.4 and luac5.1 are now checked after every future edit.